Integrated electronic piezoelectric (IEPE) accelerometers are a class of piezoelectric accelerometers that incorporate an electronic amplifier and use a single two-pole coaxial connector for both power input and signal output. The devices are also known by proprietary names such as integrated circuit piezoelectric sensor (ICP). Compared with earlier sensor interface systems requiring a charge-sensitive preamplifier external to the sensor, the use of a single coaxial connector with integrated electronics gives IEPE devices their main advantages: small size, light weight, robustness and low cabling costs. Microphones and other vibration sensors are also made using an IEPE-compatible interface.
Electrical characteristics
The IEPE interface is defined in the IEEE 1451.4 standard which also includes the definition for the Transducer Electronic Data Sheet (TEDS), data from which is carried on the same interface. Some IEPE sensors are made without TEDS, using only the powering interface defined by IEEE 1451.4. Different manufacturers' implementations vary, so the manufacturer's data sheet must be consulted for each device.
Power is supplied to the inner conductor of the coaxial cable from an external constant-current supply of 0.5 to 8 mA. The power supply can be built into the receiving instrument such as an oscilloscope or data acquisition device, or may be a separate unit.
The output signal from the device is also on the inner conductor, and consists of an AC voltage centred on a bias voltage of about 8 to 12 V. The output voltage is bounded at the lower end by the saturation voltage of the integrated IEPE amplifier (typically 0.5 to 2 volts), and at the upper end by the maximum compliance voltage of the current source (which may be anything between about 6 and 30 volts).
The shield of the cable serves as the ground return for the supply current and also protects the inner conductor from electromagnetic interference.
This method of combining the power and signal on a single pair of conductors is a form of simplex powering, sometimes referred to as phantom although it is not compatible with the phantom powering system used in audio equipment. The receiving instrument uses a simple RC filter to separate the output signal of the IEPE device from the supply current. This means that the DC component of the signal is lost, and so when a static acceleration needs to be measured, a "zero Hz" accelerometer must be used instead.