Interfacing extensometers to electronics

All strain gaged transducers (load cells, extensometers, etc.) are considered "passive" instruments.  Unlike active sensors, passive sensors typically require some sort of electrical energy (excitation) to provide an electrical output signal.   Extensometers are typically excited (powered) by a voltage of 5 or 10 VDC (although, some signal conditioners do use 5 or 10 VAC). As a result, the calibrated output of such sensors is often expressed in mV/V.   For example:  an output of 2.451 mV/V means the output at full scale, with 10 volts excitation will be 24.510 millivolts. The inspection certificate provided with your extensometer will include this data.

Since strain gage based extensometers are passive, they do require some external electronics for output. The electronics provide the excitation voltage and typically amplify the signal to a high level, DC voltage. This high level output is used for direct readout or control of the test machine. In more advanced systems the voltage output can be converted into engineering units (% strain, etc.). For use with chart recorders, the output is typically set to a specified strain/in [strain/cm] on the graph paper.

Unless some sort of device is provided to transfer the calibration to the electronics, a new extensometer will require calibration with its electronics. There are several ways to accomplish this:

• If your test controller has a strain channel built-in, we can provide an extensometer with the proper connector to allow a true plug and play situation.  However, most systems will still require some sort of calibration. 
• For data acquisition systems with a strain gage signal conditioner, a interface connector can be installed on your extensometer to allow direct connection to the system.
• For acquisition boards without signal conditioning (those that require high level inputs), Reliant can provide a calibrated, extensometer / amplifier package with an adapter cable to interface to your acquisition board.

Calibration of extensometers with electronics:

• For test controllers with a calibration system integral with their interface connector

Some manufacturers provide a system to include the extensometer's calibration in the extensometer's connector.  They usually provide for this by using shunt calibration resistor(s) and a relay or a precise span-cut potentiometer.  For these systems, calibration transfer is easily accomplished.

• Extensometer & electronics purchased  from Reliant

Extensometers purchased with electronics from Reliant are fully calibrated systems. They are factory set to display or output exact values. They are shipped "ready to use" and require no further calibration. Periodic re-calibration can be done by Reliant or most any calibration service.

• With our model CES - Digital Electronic Calibrator

If you wish to calibrate extensometers yourself, Reliant's model CES Digital Electronic Calibrator is an excellent choice.  Easy to use and with high resolution, our model CES will allow you to calibrate your extensometers to your specifications.

• Calibration services and original equipment manufacturers

Any competent calibration service will have no difficulty calibrating extensometers and electronics from Reliant.   These companies can typically recalibrate the entire test system (including load cells, extensometers and other other sensors).   Please contact us if you need help locating a calibration firm near you.