4515, IEPE Sensor Simulator

The Dytran model 4515 is a sensor simulator which allows the injection of a reference calibration signal into IEPE power unit/amplifiers from signal generators to allow calibration of such devices.

Calibration of IEPE current source power unit/amplifiers cannot be accomplished by normal signal injection methods, i.e. by simply connecting a signal generator to the “input” jack of the power unit to put a reference signal into it. The input or “sensor” jack is connected to a DC voltage supply through a constant current element (cc diode or other constant current circuit). Thus, the input voltage is held at the high DC compliance voltage level unless “pulled down” by the IEPE sensor. Because of this, the DC voltage at the sensor jack will be at this high value of compliance voltage (+18 to +30 VDC depending upon the specific power unit) and no further positive swing of the input signal is possible.

Consequently, to allow injection of a calibration signal into the power unit/amplifier, a lower bias level must be established at the input to accommodate the positive and negative voltage swing of the input signal. To accomplish this, model 4515 sensor simulator contains the same MOSFET IC amplifier chip as does the IEPE sensor with the added feature that an external signal from a signal generator may be injected directly into the gate of the MOSFET. The power unit/amplifier treats this signal as if it was generated by an IEPE sensor.

Model 4515 is a compact desk top accessory measuring 3 3/4-inches wide by 3-inches deep by 1.62-inches high. It contains the same IC amplifier chip as do most of Dytran’s IEPE sensors. The amplifier is a MOSFET input source follower circuit with unit gain. Normally, in the sensor, the piezoelectric element of the sensor would be connected to the gate of this amplifier, thus serving as the signal input source. In the model 4515, the gate is AC couples to a BNC jack labeled “Gen In”, jack J1. An external signal generator is connected to this jack to inject a reference signal into the system. Another BNC jack labeled “Monitor” provides a convenient point to monitor the input signal at the exact point where it enters the power unit.

A third jack (J3) labeled “Sensor” is provided to connect to the sensor jack of the IEPE power unit. A 10-32 micro coaxial connector was chosen for this jack because this is the type of connector used on most IEPE sensors. For system checkout and calibration, it is convenient to simply transfer the cable connection from sensor to sensor simulator and proceed with the calibration without changing cables.

The power unit provides the power to operate the IC built into the sensor simulator, thus this system exactly duplicates the operation of an IEPE sensor/power unit system. Model 4515 requires no external power, as its required power comes from the IEPE power unit.