Understanding IEPE Accelerometers

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Portable balancer & Vibration analyzer Balanset-1A

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Vibration sensor

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Optical Sensor (Laser Tachometer)

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Dynamic balancer “Balanset-1A” OEM

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An IEPE accelerometer — short for Integrated Electronics Piezo-Electric, and also sold under the trademark ICP®, or described as a “voltage-mode” or “constant-current” sensor — is a piezoelectric accelerometer with miniature signal-conditioning electronics built into its own housing. Those electronics are powered by a constant current (typically 2–20 mA) delivered through the very same two-wire coaxial cable that carries the output signal back to the instrument. By converting the sensor’s tiny, high-impedance charge into a robust low-impedance voltage right at the source, the IEPE design removes the need for an external charge amplifier and lets you run ordinary, inexpensive coaxial cable over long distances without losing signal quality. This single innovation is why the IEPE sensor has become the default transducer for industrial vibration measurement.

1. Definition: What Is an IEPE Accelerometer?

At its core, every piezoelectric sensor produces an electrical charge proportional to acceleration. The problem is that this charge is generated at extremely high impedance, so it cannot be transmitted over a normal cable without picking up noise and losing amplitude. Traditional charge-mode sensors solve this with a bulky external amplifier and special low-noise cable. The IEPE accelerometer instead packages a small FET or integrated-circuit amplifier inside the sensor, so the conversion from charge to voltage happens before the signal ever leaves the housing.

The result is a sensor that behaves like a simple voltage source. It is the close cousin of the voltage-mode accelerometer and, like most modern industrial units, is usually built as a shear-mode accelerometer for stable, low-noise performance. IEPE sensors are estimated to be used in over 90% of industrial accelerometer applications — they are the everyday workhorse of condition monitoring, balancing, and troubleshooting.

2. How It Works: Power and Signal on One Cable

Internal Construction

• Piezoelectric element: generates a charge proportional to acceleration when the sensing crystal or ceramic is stressed.
• Built-in amplifier: a FET or IC stage inside the housing converts that high-impedance charge (in picocoulombs) into a low-impedance voltage (in millivolts).
• Two-conductor cable: a single coaxial line carries both the supply power and the measurement signal.

The Power and Signal Path

The trick that makes one cable do two jobs is to ride the AC vibration signal on top of a DC bias voltage:

• The instrument feeds a regulated constant current (commonly 4 mA) up the cable.
• That current powers the sensor’s internal electronics, which sit at a DC bias voltage of roughly 8–12 V.
• Mechanical vibration modulates this voltage, so the measurement appears as a small AC signal superimposed on the DC bias.
• The instrument’s input stage is AC-coupled: it blocks the DC bias and reads only the AC vibration component.

Because the signal leaves the sensor at low impedance, it is largely immune to the capacitance and triboelectric noise that plague high-impedance charge cables.

3. Key Advantages

• Simplicity: no external charge amplifier, a plain two-wire connection, ordinary coaxial cable, and fast installation.
• Long cable runs: the low-impedance output drives cables up to about 300 m (1,000 ft) with minimal degradation and no special cable.
• Noise immunity: low source impedance gives much better EMI/RFI rejection than charge mode, so IEPE sensors thrive in electrically noisy plants.
• Cost-effectiveness: eliminating charge amplifiers lowers both system and installation cost, and the sensors are an industry standard that is widely stocked.

4. Specifications and Performance

Typical Specifications

• Sensitivity: 10–100 mV/g is common, with 100 mV/g the de-facto standard for general machinery; see sensor sensitivity for how this scales output.
• Frequency range: roughly 0.5 Hz to 10 kHz, with the low-frequency limit set by the AC coupling.
• Measurement range: ±50 g to ±500 g is typical for industrial units.
• Temperature range: −50 °C to +120 °C as standard, with high-temperature versions reaching +175 °C.
• Power required: 18–30 VDC supply at a 2–20 mA constant current.

Performance Characteristics

Well-made IEPE sensors offer excellent linearity (typically under 1% error), a low noise floor, a flat frequency response across the working band, and a calibration that stays stable over years. Pairing the right sensitivity with your instrument’s input range is worth checking on the Vibration Sensor Sensitivity Calculator so the full-scale acceleration you expect does not clip the amplifier.

5. Limitations to Respect

Low-Frequency Response

Because the output is AC-coupled, a capacitor blocks DC and the response rolls off at a low-frequency corner of typically 0.5–2 Hz (the −3 dB point). An IEPE sensor therefore cannot measure true DC or very slow changes. This is no problem for most machinery running above ~300 rpm, but it becomes a real limitation on very-low-speed shafts, where a DC-capable sensor is preferable.

Temperature Limitations

The built-in electronics are the weak point in heat: standard IEPE units are limited to about 120 °C, and even high-temperature variants top out near 175 °C. Beyond that the electronics fail, which is precisely why charge-mode sensors — having no internal electronics — remain the choice above roughly 200 °C, in nuclear service, and in other extreme environments.

Ground-Loop Sensitivity

Common-mode rejection is only moderate, so differences in ground potential between sensor and instrument can inject noise. Proper grounding and, where needed, electrical isolation prevent this; with a sound installation it is rarely an issue.

6. Applications and Installation Best Practices

IEPE sensors appear almost everywhere vibration is measured: route-based monitoring with a portable data collector, permanent online systems, temporary troubleshooting hook-ups, shop and field-balancing work, and acceptance testing of new or repaired machines. In a balancing context the same IEPE channel measures both 1× amplitude and phase. A portable two-channel instrument such as the Balanset-1A reads its IEPE accelerometers in the machine’s own bearings at operating speed, computes influence coefficients, and verifies the residual unbalance against the chosen quality grade — all without a balancing machine.

Mounting Methods

How you attach the sensor directly limits its usable bandwidth — see the dedicated note on sensor mounting and the international rules in ISO 5348:

• Stud mount: best performance and the highest usable frequency (10+ kHz).
• Adhesive: good, semi-permanent performance to about 7–8 kHz.
• Magnetic: convenient and acceptable for routine monitoring to roughly 2–3 kHz.
• Handheld probe: quick screening only, with limited accuracy and bandwidth.

Cable and Power Checks

• Use quality coaxial cable, avoid crushing or sharp bends, secure it against vibration, and keep it clear of high-voltage runs.
• Verify the instrument supplies the correct constant current (2–20 mA), check the bias voltage (typically 8–12 VDC), and confirm an adequate 18–30 VDC supply.
• When in doubt, test the channel with a known-good sensor to isolate a fault between sensor, cable, and instrument.

7. IEPE vs. Other Accelerometer Types

Type	Electronics	Cabling	Best fit
IEPE / ICP®	Built-in amplifier	Simple coaxial, long runs	~95% of industrial work
Charge mode	None (needs external charge amp)	Special low-noise cable	Extreme heat (>175 °C), nuclear
MEMS	Micro-machined silicon	Often integrated/digital	Low cost, small size, DC response

Compared with charge mode, IEPE wins on simplicity and cost but gives up the ability to survive very high temperatures. Compared with MEMS, the piezoelectric IEPE offers better sensitivity, wider bandwidth, and a longer proven track record, while MEMS counters with lower cost, smaller size, and genuine DC response. For the great majority of plant machinery, the IEPE accelerometer remains the optimal balance of performance, simplicity, and cost — which is exactly why it has displaced older charge-mode and high-impedance voltage-output sensors across most standard condition-monitoring, balancing, and troubleshooting tasks.

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