Signal Conditioning Systems
http://www.fylde.com
Fylde Electronic Laboratories Ltd. has specialised in the design and manufacture of analogue instrumentation in Preston since its formation in 1964.
Its signal conditioning products concentrate on the link between the transducer and the data acquisition system. Fylde has introduced innovative and cost effective solutions to conditioning most types of transducer, and has provided top quality instruments to aerospace and vehicle manufacturers for many years.
It is independent of any particular transducer supplier, but its experience makes us well placed to recommend an appropriate transducer for your application.
Fylde's broad spread of standard instrumentation is also found in educational establishments, research centres, and in industries ranging from power generation gas turbines down to hydraulic valve production and testing.
Fylde instrumentation is constantly evolving, and as new transducers demand new techniques, Fylde has in house design and manufacturing capabilities to respond.
As well as the standard instruments, Fylde can help in the specification, design and production of custom and semi-custom instrumentation to ISO 9000 quality standards, and is constantly at work with engineers of all disciplines who demand the best in bespoke design at a realistic price.
Fylde performance today remains a benchmark for low noise analogue design.
Applications
Strain (Bridge Transducers): Strain measurement using resistive bridge transducers.
Dynamic Strain Measurement: Dynamic strain measurement using constant current energisation.
Pressure, Torque, Load: Pressure, Torque, Load measurements using resistive bridge transducers such as load cells.
Acceleration: Acceleration Measurement using piezo-electric (charge source) transducers and ICP transducers.
Vibration: Vibration measurement using tachometer transducers linked to tracking filters.
Frequency: Frequency measurements using optical or magnetic pick ups.
Temperature: Temperature measurement using RTD or thermocouples.
Displacement (Capacitance): Non-contact displacement measurement using capacitive transducers, e.g. turbine blade tip clearance measurement.
Displacement (LVDTs): Contact displacement measurement using LVDTs.
Isolation Amplifiers: Isolation Amplifiers and other techniques for handling high and medium voltage common mode signals.
Products
Micro Analog 2: Low cost per channel modular system retaining high performance for multi-channel data acquisition applications
Blue Panelled Modules: Laboratory environment modules with comprehensive features and a wide range of instrument case options.
Programmable Instrumentation: Computer controlled modules for integration into automated tests.
Vibration Monitor: Monitors velocity and displacement resonances in rotating machines or other structures.
1800 Series: Military environment (flight qualified) modules for flight test or similar harsh environment applications.
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Strain measurement using resistive bridges such as strain gauges requires an instrument which can provide the following functions:
- Bridge energisation. A highly stable voltage source is required since variations in voltage become variations in the strain signal.
- An accurate differential amplifier with good common mode rejection.
- Bridge balance function to ensure that the bridge differential signal is zero when there is zero strain.
- Bridge calibration function to shunt one arm of the bridge with a known resistance giving a related change of signal..
Other functions may be necessary in some applications. (e.g. Auto Zero, Remote Sensing, High Bandwidth, Low Pass Filtering etc.).
The FE-366-TA is a Micro Analog 2 module which may be optionally connected by USB to make a strain gauge data acquisistion system. Free FYLDE MADAQ software supplied with all USB systems includes processing of Strain Gauge parameters to give results in microStrains. Direct analog connection to other data acquisition systems can replace the USB connection option.
FE-579-TA: A bridge amplifier with high performance, simple controls, and auto-balance.
FE-379-TA: A bridge amplifier with a complete set of features controlled manually from its front panel.
FE-H379-TA: Although the FE-379-TA above is a high bandwidth amplifier, sometimes this ultra-high bandwidth (500 kHz) module is required.
FE-366-TA: When many channels of strain gauges are used, this module provides a cost effective solution. On board jumpers are used rather than front panel controls.
FE-1810: Developed specifically for flight test applications, This module is capable of operation in the most demanding environments.
FE-759-TA: A programmable module normally used in a multichannel system allowing strain measurement to be remotely controlled by a computer. This is a single channel module which allows a total of 16 programmable channels in a 19 inch system.
FE-729-TA: A dual channel programmable module which allows 32 channels of strain measurement to be remotely controlled by a computer.
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The Wheatstone bridge circuit has been the mainstay of strain gauge measurement for many years and is often configured for constant current operation. The following note describes an alternative method for deploying constant current gauge energisation which offers advantages for dynamic strain measurements.
The technique requires the application of an extremely precise and stable constant current via only 2 wires to a remote gauge. The developed dynamic signal is recovered from the same conductors by the use of an A.C. coupled amplifier having high input impedance and high common mode rejection. This method of energisation provides an excellent signal to noise ratio which combines with the simplicity of a 2 wire connection to develop a precise dynamic measurement over a large dynamic range from below 1 Hz to as high as 100 kHz. No bridge completion is required and there is no need to balance as required by Wheatstone bridge type circuits.
Schematic of a Dynamic Strain Gauge Amplifier System
How the Constant Current system works
The balanced differential Constant Current supply is preset at 5, 10 or 20 mA. The precision and stability of this current source is very high since any noise will be amplified.
The input impedance of the amplifier and the output impedance of the current sources is arranged to be sufficiently high to avoid loading the gauge and thus introducing non- linearities into the measurement.
Because the current is constant, the connections to the gauge may be long and may exhibit resistance without detriment to the calibration; i.e., the voltage developed across the gauge is dependent only on the current supplied and the resistance of the gauge.
As the gauge value changes dynamically, so a small A.C. voltage is set up which the amplifier receives without attenuation and amplifies as required. The A.C coupled amplifier is able to ignore the standing D.C. offset presented to it's inputs. The use of a balanced differential supply and high common mode rejection means that the gauge is able to move electrically by several volts positive or negative without creating interference to the signal developed at the amplifier output.
Calibration
Standard shunt calibration methods cannot be employed with A.C. coupled amplifiers, unless the shunt value can be switched in and out of circuit sufficiently rapidly to create a dynamic calibration which is in band for the amplifier frequency range.
For 1/4 bridge (single resistor element) gauges, the FE-537-SGA provides an alternative calibration method which dynamically adds a precise low resistance which directly simulates the resistance variation of the gauge.
Fortunately, calibration is straight forward with amplifiers and systems of this type, because:-
VG = I x RG
s = VG x Strain x Gauge Factor
3. The current is extremely precise.
Where
RG = gauge resistance
rl = line resistance
I = Constant Current (14.28mA)
Vl = Voltage across line resistance
VG = Voltage across gauge
The amplifier consists of the following main sections:-
2. Constant Current Strain Gauge Supply
3. AC Coupled Low Noise Amplifier
4. Low Pass Filter
5. High Pass Filter
6. Output Stage
7. Calibration Circuit
8. Overload Circuit
The FE-1823 Dynamic Strain Gauge Amplifier
The FE-1823 Dynamic Strain Gauge Amplifier is a standard module in the FYLDE 1800 series range of instrumentation modules. It provides two channels of energisation and amplification and is suitable for use in demanding environments such as flight test.
Strain measurement using resistive bridges such as strain gauges requires an instrument which can provide the following functions:
- Bridge energisation. A highly stable voltage source is required since variations in voltage become variations in the strain signal.
- An accurate differential amplifier with good common mode rejection.
- Bridge balance function to ensure that the bridge differential signal is zero when there is zero strain.
- Bridge calibration function to shunt one arm of the bridge with a known resistance giving a related change of signal.
The FE-366-TA is a Micro Analog 2 module which may be optionally connected by USB to make a strain gauge data acquisistion system. Free FYLDE MADAQ software supplied with all USB systems includes processing of Strain Gauge parameters to give results in microStrains. Direct analog connection to other data acquisition systems can replace the USB connection option.
Bridge Amplifiers
FE-379-TA: A bridge amplifier with a complete set of features controlled manually from its front panel.
FE-H379-TA: Although the FE-379-TA above is a high bandwidth amplifier, sometimes this ultra-high bandwidth (500 kHz) module is required.
FE-366-TA: When many channels of strain gauges are used, this module provides a cost effective solution. On board jumpers are used rather than front panel controls.
FE-1810: Developed specifically for flight test applications, This module is capable of operation in the most demanding environments.
FE-759-TA: A programmable module normally used in a multichannel system allowing strain measurement to be remotely controlled by a computer. This is a single channel module which allows a total of 16 programmable channels in a 19 inch system.
FE-729-TA: A dual channel programmable module which allows 32 channels of strain measurement to be remotely controlled by a computer.
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Charge amplifiers have traditionally been employed to interface transducers which output a charge level in proportion to mechanical stimulus. Such transducers are known as Piezo-Electric and include devices to measure acceleration, pressure, force and sound. In recent years, due to improvements in micro-electronics, a challenge has emerged in the form of transducers with inbuilt charge to voltage conversion. Such devices are generally powered by utilisation of the same (coaxial) cable which conducts the signal to the receiving instrumentation. So advantageous is the technique, being low cost in both cabling and receiving electronics, that many manufacturers offer a complete range of transducers operating on the constant current, Integrated Circuit Piezo (ICP) principle.
Schematic of an Amplifier System
Mode of Operation
The output of the transducer electronics is biased to a voltage which is approximately half of the power supply capability. As this is typically 20-24VDC , the bias level is often in the region of 10-12VDC.
When the transducer develops a dynamic signal, this is superimposed on the bias level to give an AC voltage which may range from a few milli-volts to several volts in amplitude. The bias level may be monitored by the receiving amplifier in order to provide information on both transducer and cable status.
It should be appreciated that this technique is generally favoured for dynamic signals when AC coupling is acceptable, although receiving electronics with DC performance is available for specialist application.
Fylde offers receiving amplifiers in several forms; all have constant current supply for the transducer, high impedance amplification and configurable low pass filter.
In addition, the FE-530-IE and FE-376-IPF are available with a unique input circuit which is able to reject interference which may arise when transducers must be electrically earthed to a structure.
The FE-376-IPF is a Micro Analog 2 module which can be connected by USB to make an acceleration or vibration data acquisistion system. Free FYLDE MADAQ software supplied with all USB systems includes processing of signals to providing the FFT spectrum of the acquired data.
| Blue Panel System | FE530IE | Features LED bias monitoring |
| Micro Analog 2 | FE-376-IPF | Low cost dual channel card |
| 1800 Series | FE-1817 |
High integrity dual amplifier for aircraft or automotive apps |
Converting Piezo Transducers
Many applications remain for standard piezo-electric transducers because of :-
| Cost. | They may be cheaper than an equivalent integrated electronic type. |
| Size. | They may be smaller than an equivalent integrated electronic type. |
| Environment. | They can often withstand a higher operating temperature. |
Where it is necessary to instrument these transducers, charge amplifiers are often the first choice. However, the constant current technique may still be used by utilisation of an inline or Head Amplifier. These miniaturised devices are often themselves charge amplifiers which are specially configured to operate on the constant current power supply principle and may be obtained pre-calibrated to exactly convert pico-coulombs to milli-volts.
In this case, the transducer must be connected to the head amplifier using low noise 100% screened charge amplifier cable, and thus it is cost and also performance effective to keep this section of cabling as short as is practicable. Between 1 metre and 5 metres of cable will prove to be sufficient in most installations. These inline amplifiers will often prove to be small enough not to require specific housing, and may be left hanging in the cable harness.
Important points to note here are that the cable type changes either side of the head amplifier, and that calibration is very straightforward when head amplifiers are given exact conversion ratios. For example, figures such as 1 mV/pC and 10mV/pC conversion ratios ensure error free calibration, and importantly, enable amplifiers to be exchanged or swapped at will.
Fylde Head Amplifiers
Fylde offers Constant Current Head Amplifiers in several types:
| True Charge Amplifier | FE-074-HA/C | Pre-calibrated 1mV or 10mV / pC | |
|
Passive Charge Amplifier |
FE-074-HA | 0.1mV / pC for high charge levels | |
| Buffer Amplifier | FE-665-DIC | Low cost unity gain | |
These inline amplifiers are small, rugged and easy to apply. All operate from a constant current supply and will convert a Piezo Electric transducer to voltage output.
Notes relating to Cables
1. Cable from Transducer or Head Amp to Receiving Amplifier
The transducer (having built in amplifier), or head amplifier may be required to drive cable lengths up to a hundred metres or more. In these instances, consideration of the drive requirements is worthwhile. The cable capacity, coupled with the device output impedance, forms a low pass filter whose cut off frequency may preclude the passage of frequencies of interest according to the formula:
| Fc = 1/2piCR | Where | Fc = Low pass cut off frequency |
| C = Cable Capacitance | ||
| R = R1 + R2 = Device output impedance and driver restrictions* |
*The device output impedance (R1) is generally designed to match the characteristic impedance of the expected cable type; typically 50 -100. However, the device's cable drive ability is limited by the constant current supplied by the receiving amplifier, and further restricted because only a portion of that current is available to drive the cable, the remainder being consumed within the device electronics. This parameter is described by the formula :-
| R2 = V / I | Where | V = signal pk voltage |
| I = constant current (less 1.5mA) |
Thus, satisfactory performance of the arrangement depends on : -
| i) | The cable length |
| ii) | The peak voltage of the signal |
| iii) | The maximum frequency of interest |
| iv) | The current available to the transducer or head amplifier |
| v) | The output impedance of the transducer or head amplifier |
As an example, consider the case of a transducer connected by 100m of miniature RG59 coaxial cable of capacitance 50pF/m. Maximum signal voltage is in the region of 5Vpk and supply current is 4mA
| R2 | = | 5 / (4-1.5)mA = 2kohm | |
| Fc | = |
1 / 2pi x 5000pF x (50* + 2k)ohm |
*Device o/p impedance |
| = | 15.5kHz |
Peak voltages at greater than 75kHz may be passed if their amplitudes are restricted to 1V or less.
Of course, many signals are complex and although the fundamental may be relatively low in frequency, inherent harmonics may raise the frequency requirement to many times the fundamental; fortunately, often at greatly reduced amplitudes.
2. Input Cables from Piezo Transducers to Head Amplifier
2.1 True Charge Head Amplifiers
One of the characteristics of the classic charge amplifier configuration is that it is able to operate using long input cables without calibration error; the only downside being the cost of the special input cables required. Noise performance suffers as cable length increases but typically this is as little as 0.05pC / 10m of additional cable.
Thus where head amplifiers with charge amplifier input stages are in use, cable length will cause little or no change in calibration.
2.2 Buffer Head Amplifiers
Caution should be exercised however if buffer head amplifiers are deployed. These simple devices are high impedance voltage buffers and their calibration may be compromised by change of input cable length. Why this should be is explained in the following:-
The operation of buffer type devices relies on the fact that the equivalent circuit of a Piezo Electric transducer can be simplified to a voltage generator in series with a capacitor. Transducer capacitance may range in value from a couple of hundred pF to several thousand pF.
Because the buffer amplifier is sensitive to the voltage developed and not strictly the charge output of the transducer, a voltage divider is developed in the ratio of transducer capacitance CT to cable capacitance Cc. Cable capacitance varies with mechanical parameters but a values of 90pF / metre is typical.
| Example: | Transducer Charge Output | = | 31.6pC/g |
| Transducer Capacitance ( CT) | = | 1000pF | |
| Cable length 2m. (CC) | = | 180pF |
The voltage output of the transducer may be calculated by using the formula V = Q/C
| For the example above: | V | = | 31.6pC / 1000pF |
| V | = | 31.6 mV / g |
When a 2 m cable is added, the voltage seen at the buffer amplifier (v) becomes :-
| v | = | V x CT / (CT + Cc) |
| v | = | 31.6 x 1000 / 180 |
| v | = | 26.8 mV / g |
This desensitisation is not a problem providing that a calculation similar to the above is performed to determine loss of signal level, but beware, transducer manufacturers may regard the voltage output of their devices as being of secondary importance. Also, the capacitance given for the transducer in the data sheet, if given at all, may be a nominal figure. Calculation is fine for estimation of output level, but for highest accuracy the transducer and buffer amplifier system should be through calibrated using a mechanical method such as a vibration table.
It follows from the above that changing the cable length will change the output voltage and cables should only be replaced by ones of similar length and type to avoid having to recalculate / recalibrate.
On the positive side, buffer amplifiers are low cost and very small size, also their simplicity makes for high reliability.
2.3 Passive Charge Amplifiers
When charge levels from piezo transducers are high, a passive charge amplifier may be deployed.
Such devices provide a large receiving capacitor which accepts the source charge with minimum error.
In this configuration, the transducer charge is shared between the transducer capacitance, cable capacitance and amplifier input capacitance. Because the amplifier capacitance is made dominant, the voltage (V) developed at the amplifier input is controlled largely by Ci.
V = Q / C Where C = CT + Cc + Ci
These amplifiers are best employed when charge levels exceed 10000pC; such levels may originate in shock measurements or pressure events.
After through calibration, errors can exist when transducer or cable capacity is changed; these can often be kept small however, as the following example explains:-
| Example: | Consider a pressure transducer transducer which outputs 15pC / psi with an expected maximum pressure of 5000psi. Transducer capacity is 1300pF; cable length is 2 metres at 100 pC / m. The input capacitance of the amplifier is 100nF. |
| Therefore | CT | = | 1300 pF | |
| Cc | = | 200 pF | ||
| Ci | = | 100,000 pF | ||
| Input voltage to the amplifier is:- | V | = | Q/C | |
| = | (15 x 5000pC) / 101500pF | |||
| = | 0.739V |
A change in the transducer capacitance from 1300pF to 1500pF, or a change in the input cable length from 2m to 4m would result in an error of only 0.2%.
Fylde have supplied vibration monitor systems to the Aero engine industry for since the 1970s, and our current range of vibration monitoring modules builds on our proven technology which is in use in engine ground test facilities worldwide. Although proven in aero engine applications, rotating machinery in general has vibration characteristics which can be monitored using data gathered from strategically located accelerometers.
Fylde's vibration monitors are modular, so a large number of system configurations are possible, but most systems have one or more of the following features.
- Filters tuned to specific harmonics of the rotation frequency to pick out vibration characteristics.
- Indicators and Alarms when specific threshold levels are detected.
- A self test feature to simulate specific acceleration signals for self calibration and health checking.
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Generally referred to as frequency to voltage conversion, the principal features of frequency measurement are as follows:
- Rejection of noise (often referred to as false triggering).
- Configurable speed of response to change of signal frequency. (filtering)
- Accuracy of measurement. (timing accuracy)
Note that the FE-578-FV can be set by the user to any full scale frequency. The FE-396-FV has a number of jumper selectable frequency ranges from 50 Hz to 20 kHz. The FE-396-FV is a Micro Analog 2 module which can be connected by USB to make a frequency data acquisistion system. Free FYLDE MADAQ software is supplied with all USB systems.
A single channel module with an instantaneous response to change of input frequency. This module needs only one cycle of the input frequency to produce the output voltage. It is suitable for all types of frequency measurement from 10Hz to 50 kHz.
FE-396-FV:
This is a two channel module in the micro-analog 2 style. It uses on board jumpers to select both the full scale frequency and the speed of response. It is an extremely versatile module combining low cost, accuracy, and speed of response
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Fylde offer modular instruments for temperature measurement from both thermocouple and RTD (Resistance Temperature Device) sensors.
Instruments to develop a voltage proportional to temperature from thermocouple sensors typically provide the following features:
- Measurement of the temperature at the local (cold junction)
- Correction of the thermocouple voltage to give a voltage relative to absolute temperature.
- Linearisation and amplification of the absolute thermocouple voltage
- Scaling of output voltage to be proportional to temperature.
Fylde's thermocouple signal conditioning modules use analogue computation techniques for linearisation, hence they are able to provide a very fast response to sudden changes in input signal. Although they are suitable for general use, this makes them capable of fast rise time temperature studies (e.g. engine combustion chambers or explosive devices.)
Thermocouple Signal Conditioning
Note that the FE-363-TCL is available linearised for one four temperature ranges for K type thermocouples only. The FE-386-TC has a number of jumper selectable temperature ranges and again is linearised for K type thermocouples only.
The FE-386-TC is a Micro Analog 2 module which can be connected by USB to make a temperature data acquisistion system. Free FYLDE MADAQ software is supplied with all USB systems.
FE-363-TCL:
A single channel module for K type thermocouples with a factory set temperature range. This type of module is supplied in a case for which the user can specify an input connector type.
FE-386-TC:
A dual channel module for K type thermocouples with jumper selectable temperature ranges. This is a Micro-Analog 2 module which means that the case must be fitted with the screw terminal thermocouple adapter CA-386-TC. The adapter contains the sensor for the cold junction temperature.
RTD (Resistance Temperature Device) Signal Conditioning
RTD devices have a precise resistance v temperature relationship. If you have a Fylde FE-379-TA module, it can be used to energise the RTD with a constant current and measure the voltage across the device.
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Click to enlarge
Introduction
The FE-419-CDT and the FE-420-CD enable the measurement of displacement by use of a capacitance technique. The method relies on a special configuration of a charge amplifier circuit to enable the measurement using concentric guarded probes.
These amplifiers are designed to operate together with the FE-411-OSC in a capacitance measurement system. In multi-channel systems, one oscillator will energise as many as 16 channels of amplifiers. (Fig. 1 shows a single channel system.)
Capacitance probes, specifically designed to connect via 100% guarded cable, enable the system to generate voltage signals proportional to the distance between the probe and an earthed conductive target.
Capacitance probes generally carry a guard ring enabling a linear relationship to be maintained between distance and voltage output of the system. Smaller probes can be realized by sacrificing guard area when a linear relationship of distance to output is not essential or when calibration of the system allows.
The amplifiers output a linear voltage against distance characteristic. In the case of the FE-419-CDT, a voltage against capacitance output may also be made available.
Fylde offer two types of amplifier ; each will operate with the FE-411-OSC. The technique for each amplifier is marginally different and each is suited to particular transducer ranges and cables.
FE-419-CDT
The FE-419-CDT is better suited to applications where the capacitance returned from the probe is likely to be greater than 0.2 pF. Larger transducers generate larger capacitances and so the FE-419-CDT will operate more optimally with probes greater than 2 mm diameter. Operation with 2 mm probes is still possible, but with this probe the noise in the measurement will usually be 10 dB worse than when using the FE-420-CDT. On the positive side, the FE-419-CDT is able to operate with cable lengths of up to 10 m even in installations employing triaxial cables. The technique is robust and adaptable and can be applied on probes from 2 mm up to many centimeters in diameter.
A ruggedised version of the FE-419-CDT exists ; the FE-486-OCAM is a 4 channel amplifier in an IP65 sealed enclosure for operation in harsh environments.
FE-420-CD
This amplifier is at its best with small transducers. A capacitance of 1 pF should be considered as the upper limit and this rules out 8 mm transducers at closer than 0.5 mm range. Noise will often be lower for a given bandwidth when using this amplifier and it should be selected for 2 mm transducers unless input cable length ( max 4 m) precludes it. The FE-420-CD is able to operate with special versions of the FE-411-OSC with a frequency of 32 kHz. ; the resulting measurement bandwidth is 12 kHz.
Capacitance Probes
These are available from Fylde in 3 sizes ; each is generally known by the size of its inner electrode. The diameter of the inner electrode limits the transducer's operating range. In general, the probes will give a linear output at a range equal to the diameter of the inner electrode :
| 2 mm diameter probe | Linear range 2 mm | Absolute range 4 mm (typical) |
| 4 mm diameter probe | Linear range 4 mm | Absolute range 8 mm (typical) |
| 8 mm diameter probe | Linear range 8 mm | Absolute range 16 mm (typical) |
Transducer, Cable and Connector
4 mm Probe and microdot connector
The input cable must be 100% screened carbon filled low noise cable. The outer screen is not an earthed screen and is only connected to the transducer guard ring to maintain the total screening between amplifier and transducer. A microdot connector is used from the front panel of the amplifier. In certain circumstances the user may wish to design his own transducer arrangement; Fylde are able to help in the design of the customer's own transducers. Please contact the factory for advice.
Linearity
The linearity of the measurement depends on factors involving the transducer design, the operating range and the target geometry. In general, a linearity of ±1% of full scale is achievable under typical operating conditions; thus an amplifier and probe configured for a range of 2 mm full scale will be linear to ±20 µm at up to 2 mm distance.
Dynamic Considerations
One of the attractions of the capacitance technique is that it offers good bandwidth in the measurement. A typical bandwidth setting for the measurement is 1 kHz (rise time 300 µs) but bandwidths up to 12 kHz are possible (FE-420-CD only).
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A device which can measure displacement using the relative position of two inductors is called an LVDT (Linear Variable Displacement Transducer.) These devices typically have a moving part (usually a rod) which attaches to the test point and a fixed part : both parts carry one or more inductors.
Some devices have built in electronics requiring only a steady (DC) voltage to energise them and giving a relatively friendly output often scaled in V/mm.
The following modules are suitable for use with DC LVDTs.
Bridge Amplifiers for use with DC LVDTs
FE-379-TA:
A bridge amplifier with a complete set of features controlled manually from its front panel.
FE-366-TA:
When many channels of DC LVDTs are used, this module provides a cost effective solution. On board jumpers are used rather than front panel controls.
Some LVDTs do not have built in electronics and have to be energised by a varying (AC) voltage which couples from the fixed inductor to the moving inductor. The strength of the coupling is proportional to the relative displacement of the two inductors. Special modules called Carrier Amplifiers are used to carry out this signal conditioning.
Carrier Amplifiers
FE-346-CA:
A dual channel module with on board jumpers to set the gain. Front edge controls are provided for balance and gain adjustment. Each channel shares the same 3 kHz oscillator.
The FE-366-TA bridge amplifier and FE-346-CA carrier amplifier units are Micro Analog 2 modules which can be connected by USB to make a displacement data acquisistion system. Free FYLDE MADAQ software is supplied with all USB systems.
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An isolation amplifier is a device which can measure the voltage between two terminals while maintaining a physical barrier between the test points and the terminal at which the measured voltage is presented.
Isolation amplfiers are typically used in the following situations.
Note that many Fylde products have a high common mode range and / or high input impedance with excellent common mode rejection properties. In general such amplifiers will give superior performance to isolation amplifiers although the safety of the measurement installation must always be the primary consideration.
FE-560-IA:
The FE-560-IA is a high voltage isolation amplifier and attenuator providing galvanic isolation of up to 1.5 kV isolation between signal earth and output earth. The amplifier has gains from 1/100 up to x 100 with gain accuracy typically +/-0.1% for all steps. Isolation mode rejection is better than 150 dB (at gain 100). A 3 pole active filter is included, set by a plug in resistor network, the isolation amplifier is capable of operation up to 50kHz.
Micro Analog 2 is a low cost multi-channel solution which addresses all signal conditioning requirements using a range of plug in modules and enclosures. . Fit any combination of signal conditioning modules for application with the chosen sensor type. Screw on the rear panel adaptor if one is needed for your sensor. Add the USB data acquisition module to connect directly to your PC or use the BNC and other adaptors to connect to your data acquisition equipment.
- Load Cells
- Pressure Transducers
- AC and DC LVDTs
- Accelerometers
- Thermocouples
- Frequency Pickups
...
FE-MM40 (40ch)
- 2U Rack or Bench Mount
- USB data acquisition
- DC powered
- USB data acquisition
FE-MM8 (8 ch)
- DC powered
- USB data acquisition
- Rugged and Portable
- DC powered
- Most compact USB data acquisition
- Highest sample rate (100 kHz each channel
- 2U Rack or Bench Mount
- Mains powered
Plug-in Modules
- FE-H366-TA High Bandwidth Bridge Transducer Amplifier
- FE-366-AC AC Amplifier
- FE-346-CA Carrier Amplifier
- FE-356-OA General Purpose Amplifier
- FE-376-IP Accelerometer Amplifier
- FE-386-TC Thermocouple Amplifier
- FE-396-FV Frequency to Voltage Converter
Connectors
- CA-386-TC CJC for Thermocouples
- CA-376-IP Coaxial Input Connectors
- FE-MAC-40C 40 BNC outputs
- FE-MAC-8C 8 BNC Outputs
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The range of FYLDE blue panelled modules provides a very wide range of solutions to signal conditioning requirements. Stability of the measurement and flexibility of application are the key features and systems comprising these modules also provide very high reliability due to complete inter-channel isolation. A range of instrument case formats complements the available module types and any mixture of modules to fit any case format may be chosen. All modules have 10 V outputs with facilities to scale the output to suit the connecting equipment.
The following are a selection from the available types.
Bridge /Transducer Amplifier FE-379-TA The latest in a line of transducer amplifiers providing features demanded by our customer's experiences of decades of D.C. bridge applications. The bridge supply is capable of operation with Zener barriers. Two sets of on board bridge completion, high performance preamplifier, averaging auto-zero, comprehensive limit detection and wide range active filter are standard. Options include , 4-20 mA output, 8 pole filter, isolation or other high level output conditioning.
IEPE Receiver and AC coupled Amplifier FE-530-IE This module is for use with IEPE transducers, but may also be used as an AC coupled difefrential amplifier. It provides a choice of 4 mA or 8 mA power to the transducer with bias level monitoring. As an amplifier it has bandwidth from 0.16 Hz to > 70 kHz and featuires an 8 pole low pass filter and 2 pole high pass filter. Front panel control is complemented by an RS232C programmable option. For Charge Transducers a suitable head amplifier is the FE-074-HA/C.
Dynamic Strain Gauge Amplifier FE-537-SGA The FE-537-SGA energises a remote strain gauge with an exact constant current. This allows a simple two wire connection over any distance to a standard 1/4 bridge gauge. (4 wire connection to full bridge transducers is also possible.) The dynamic signal is AC coupled and precisely amplified. The module provides an 8 pole active filter which may be set by a resistor network. Frequency response extends from < 1 Hz to > 50 kHz.
Differential D.C. Amplifier FE-351-UA Offering very low noise and drift performance, this differential d.c. pre-amplifier has a gain range from x0.2 to x10,000 (�0.1%) using switched attenuator and switched and vernier gain controls. Offset and calibration controls are provided. An on board auxiliary socket can accept a plug in 4 pole low pass filter. A front panel LED illuminates when fitted.
Isolation Amplifier FE-560-IAThe FE-560-IA is a high voltage isolation amplifier and attenuator providing galvanic isolation of up to 1500V DC or peak between signal earth and output earth. The amplifier has gains from 1/100 up to x 100 with gain accuracy typically +/-0.1% for all steps. Isolation mode rejection is better than 150 dB (at gain 100). A 3 pole active filter is included, set by a plug in resistor network, the isolation amplifier is capable of operation up to 50kHz.
This "instantaneous" frequency-voltage converter responds almost immediately to a variation in rate of incoming pulses, e.g. when applied with a magnetic or optical pick-up . The unit is suited to any frequency measurement from 10Hz up to 50 kHz. Exceptional accuracy and linearity are combined with the very fast response to each edge of the frequency signal.
Tracking Filter FE-3051-TF The FE-3051-TF is a frequency controlled tracking bandpass filter with a range of 20Hz to 1kHz, intended for application in vibration measurement. A Tachometer input may be connected via a conditioner and divider module (FE-579-FD) to allow the Tracking Filter to be centered at harmonics of the rotational speed .
Bridge /Transducer Amplifier FE-H379-TA When high frequency results from D.C. bridge transducers are required, this Transducer Amplifier provides 500kHz bandwidth at 3V RMS. The module provides 0.5 V to 12 V constant voltage supply at 50 mA with balance indicators and bridge completion facilities. The comprehensive controls include balance and auto-zero, switched filter, shunt calibration, output calibration, and output scaling.
Charge Amplifier FE-128-CAHigh performance charge amplifier with calibrated controls, covering the range 1pC to 50,000pC and developing �10V output. The amplifier has good L.F. response and quasi-static performance with high frequency response up to 100 kHz. A range switch and calibrated ten turn dial match the unit to the transducer sensitivity. A separate switch allows the number of mechanical units per volt of output to be set. The module's low pass filter cut off frequency is easily changed using a plug in resistor pack. . A compatible wide range integrator is available - see FE-294-IA.
This module is similar to the standard FE-128-CA but converts higher charge signals (up to 500,000 pC for 10V output.)
Capacitance Displacement Amplifier FE-419-CDT Designed for measurements up to 1 kHz in high temperature environments where long cables (coax or triax) are often necessary. The FE-419-CDT overcomes the difficulties of operating guarded capacitive sensors to measure clearances in applications such as turbines. The output is proportional to distance from the target and standard modules operate with transducers with target capacitance ranging from 2.5 pF down to 0.025 pF. A compatible oscillator e.g. FE-411-OSC is required.
Capacitance Displacement Amplifier FE-420-CDThis module differs from the FE-419-CDT in giving greater sensitivity at the expense of reduced tolerance of cable capacitance. (2 m cable lengths are recommended.) Measurement distance depends mainly on the transducer type and can range from microns to centimetres. It is suited to applications involving extremely small distance variations and fast rise times. A compatible oscillator e.g. FE-411-OSC is required.
Switched Active Filter FE-301-SFWhen there is a need to remove unwanted high or low frequency noise from any signal, or when measurements must be carried out at specific bandwidths, a filter may be required. We offer filters of from 2 to 8 poles using Butterworth, Bessel or Chebyschev type response in high-pass or low-pass form. In addition it is possible to provide an input buffer which may be differential or single ended with or without gain or attenuation. A simple fixed frequency filter (i.e. without the front panel rotary switch) can also be chosen.
Charge Head Amplifier FE-074-HA/CThis true charge head amplifier can operate with long input cables and variations in input capacitance. It is available with sensitivities of 1 mV/pC or 10 mV/pC.
The FE-077-DCA is intended for use with double ended (differential) accelerometers typically used for machine vibration monitoring. This is an ICP device powered by a current in a coaxial cable which also carries the signal to the receiver amplifier. For a compatible receiver amplifier, see the FE-530-IE.
A 16-channel digital monitor, the M6-DS is ideal for use in any system where it will monitor the outputs and/or transducer supply from up to 16 modules. The module can measure a.c. with its built in precision rectifier scaled for RMS and also features a peak hold function. A front panel BNC socket enables additional monitoring equipment to be easily connected into circuit.
One of a range of instrument cases, this case accepts up to two one inch wide modules or a single two inch wide module. Power may be D.C. or mains A.C.
One of a range of instrument cases, this case accepts up to four one inch wide modules or two two inch wide modules. Power may be D.C. or mains A.C.
One of a range of instrument cases, this case accepts up to eight one inch wide modules or four two inch wide modules. Power may be D.C. or mains A.C. This unit may also be rack or panel mounted if required.
One of a range of instrument cases, this case accepts any combination of modules up to the full aperture width. Power may be D.C. or mains A.C. The unit is suitable for rack mounting using an optional rack mounting kit.
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Programmable instrumentation is signal conditioning which is controlled only by a computer. The front panel controls are either not provided or can be "locked out" by the computer.
Programmable instrumentation is typically used in test installations which perform routine tasks for which a computer must have control over the instrumentation settings. If the instrumentation settings are fixed, standard instrumentation such as Micro Analog 2 can be used.
The computer usually needs to achieve both control over the instrument and to acquire the conditioned signals. In Fylde's programmable instrumentation the control uses the computer's RS232C or Ethernet interface. The computer acquires the conditioned signals using a separate data acquisition system.
Integration of test software such as National Instruments LabView, Keithley's TestPoint, or HP's Vee with Fylde's programmable signal conditioning equipment is simple because the commands to control the instrument conform to the IEEE 488.2 standard. In addition Fylde provide software drivers for National Instruments' LabView.
The following signal conditioning modules are available.
FE-759-TA: A single channel strain gauge amplifier with comprehensive programmable features.
FE-729-TA: A dual channel strain gauge amplifier with a reduced set of features compared to the FE-759-TA.
FE-768-PF: A programmable Low Pass, High Pass, or Band Pass 8 pole filter module.
FE-859-TA: A programmable AC/DC transducer amplifier with both constant current and constant voltage transducer supplies.
FE-859-HA: When used together with the FE-859-HA, this module adds the capability to use both Charge mode and IEPE mode accelerometers to provide a comprehensive signal conditioning system.
Rear panels are normally fitted with input connectors and output connectors which are user specified since each system sub-rack is built to order. This allows users to specify the correct connector type for the computer's data acquisition system.
The FE-859-RA is a rack system which combines the FE-859-TA and FE-859-HA modules.
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All rotating machines or vibrating structures will exhibit resonances. i.e. Maximum amplitudes of velocity or displacement which occur at some characteristic vibration frequency. By using an accelerometer located at the point of the structure to be monitored and a suitable pick-up for the driving frequency, the basic data to derive velocity and displacement amplitudes can be obtained. It is possible to tune to harmonics of the driving frequency and monitor amplitudes thus providing a characteristic signature for the behaviour of the structure.
This family of FYLDE modules form the components for any vibration monitoring system. The main illustration shows a typical system which handles two accelerometers and can be tuned to simultaneously monitor four separate harmonics.
The FE-3051-TF is a frequency controlled tracking bandpass filter with a standard range of 20 Hz to 1 kHz. (lower frequency ranges may be specified if required.) The tracking filter may be connected via the Tracking Ratio Adaptor (FE-3061-TA) to be centered at harmonics of the rotational speed. The filter gives an AC output at unity gain, and also a rectified and filtered DC output at 1 V DC for 1 V AC.
The Tracking Ratio Adaptor satisfies the requirement to tune the system's FE-3051-TF tracking filters to harmonics which may be fractions or multiples of a fundamental frequency. This unit accepts the fundamental frequency input from a tachometer transducer which may be a magnetic pick-up or other transducer type. It provides optical isolation and synthesizes an appropriate harmonic frequency from multiply/division factors set by banks of on board switches.
This module sets the highest frequency of interest for the application. It is a fixed, user specified frequency with the value marked on the front panel. The pass band is unity gain and the frequency response is 6 pole Butterworth which provides very low in band ripple.
This module sets the lowest frequency of interest for the application. It is a fixed, user specified frequency with the value marked on the front panel. The pass band is unity gain and the frequency response is 6 pole Butterworth which provides very low in band ripple. A special dual frequency version is available.
This module may be set to an input range of 10, 20 or 50 pC/g. A precision integrator provides a velocity output in addition to the acceleration output. The acceleration output is scaled at 10 mV RMS / g (peak) and the velocity output is scaled at 2 mV RMS / mm/s (peak). A front panel control allows the module to substitute the system self test signal for the input signal providing through calibration.
The FE-554-IRM incorporates scaling and integrator functions to provide both velocity and displacement outputs in metric units (mm/s and micro m). Systems requiring scaling in imperial units (in/s and mils) may use the alternative FE-554-IRI module.
This module produces a precision sine wave simulating a velocity and displacement signal. This signal is routed directly to the input of the system's charge amplifiers allowing complete system validation and calibration. The signal is also routed to the Tracking Ratio Adaptor(s) allowing stable self test outputs to be generated by the Tracking Filter(s).
This module incorporates the system power supply for all modules in the system. Two indicating meters enable monitoring of N1, N2 and Broad Band signal levels for two channels. The power supply operates from 110V or 230V ac 50/60Hz
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The Fylde 1800 series is uncompromisingly designed to meet the need for a high channel density modular analogue signal conditioning system capable of operating in the most demanding of vehicle (including aircraft) environments. It has a proven history of use in flight test and motor vehicle applications measuring precise mechanical parameters. A comprehensive set of data sheets for all modules are available for download.
Dual Bridge / Transducer Amplifier FE1810The bridge power supply generated by the system is combined with the on board bridge completion and instrumentation amplifier to provide two channels of high quality bridge amplification.
This single channel module has front panel controls including a bridge balance system and shunt calibration system.
The module incorporates constant current sources for transducer excitation and provides two channels of dynamic amplification including configurable three pole filters.
When strain gauges are excited by a very precise and low noise constant current, two wire connection to the gauge provides excellent dynamic results.
This module includes cold junction compensation and linearisation for K type thermocouples. Measurement range is -50°C to +1000°C.
This module measures the RMS amplitude of input waveforms. Bandwidth is from 15.9 Hz to 50 kHz.
This system case is constructed from machined aluminium and occupies a small envelope (180 W x 76 H x 108 D) It can accept up to 8 dual channel modules to provide a very compact 16 channel signal conditioning system.
Where only one or two channels are required in a small space, this chassis allows a power supply and signal conditioning module to be combined in an envelope of only 36 W x 66 H x 88 D.
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