Integrated Electronics Piezo-Electric
The abbreviation IEPE stands for Integrated Electronics Piezo Electric . It denotes an industrial standard for piezoelectric sensors with built-in impedance converter electronics. These can be acceleration , force and pressure sensors . The IEPE standard is also used for measurement microphones . Different manufacturers also market the IEPE principle under proprietary names such as ICP ( integrated circuit piezoelectric ), CCLD ( constant-current line-drive ), IsoTron or DeltaTron .
The IEPE sensor electronics, mostly implemented as an FET circuit, convert the high-impedance signal from the piezoelectric material into a voltage signal with a low impedance of around 100 Ω . A low-impedance sensor signal is advantageous because it can be transmitted over long lines with little loss. In addition, the low-noise special cables otherwise required for piezoelectric sensors can be dispensed with.
The special feature of the IEPE principle is that the supply current and the sensor signal are transmitted together via a simple coaxial cable.
The sensor electronics are supplied with a constant current, which is usually between 2 and 20 mA . The higher the current, the greater the permissible cable length. Most measuring devices with IEPE inputs provide 4 mA.
When supplied with constant current, a positive operating point voltage , which is typically 8 to 12 V , forms across the sensor . The actual measuring signal of the sensor is superimposed as an alternating voltage with this operating point voltage. The bias voltage of the power source is usually between 24 and 30 V, so that a symmetrical modulation in positive and negative direction is achieved.
A typical IEPE supply with 4 mA constant current from a voltage source with 25 V has a power consumption of around 100 mW. This can be a disadvantage in battery-operated measuring devices. This is why there are low-power IEPE sensors that work with a constant current of 0.1 mA from 12 V. The power consumption can thus be reduced by up to 90%.
The operating point voltage is often used in measuring devices with an IEPE input for sensor detection. If it is close to the constant current source supply voltage, there is no sensor or the cable is interrupted. If it is at saturation voltage, there is a short circuit in the sensor or cable. A functioning sensor is detected in the area in between. The operating point voltage is kept away from the measuring device input with a coupling capacitor and only the signal voltage of the sensor is processed further. The IEPE constant current supply is integrated into the inputs of many measuring devices that work with piezoelectric sensors or measuring microphones.
Piezoelectric sensors without IEPE electronics, i.e. with a charge output, are reserved for applications that require very low frequencies, high operating temperatures, an extremely large dynamic range, very energy-saving operation or an extremely small design.