Moving-Coil vs Piezoelectric Velocity Sensors: Replacement Checks

Before replacing a vibration velocity sensor, identify the signal expected by its monitor. A moving-coil pickup, a piezoelectric velocity sensor and a 4–20 mA velocity transmitter can all describe machine vibration in velocity units, but their electrical connections and the information they deliver differ. A matching connector or sensitivity number does not establish interchangeability.

This guide concerns vibration at a bearing housing or machine casing. It does not concern rotational speed in rpm. For the measurement location, see shaft vibration versus casing vibration; for pulses and rotational-speed inputs, use the speed-sensor guide.

Start with the complete sensor code and the receiving channel's model, wiring diagram and configuration. Those details are more useful for a replacement review than a request for an unspecified equivalent.

A moving-coil velocity pickup uses relative movement between a coil and a magnetic field to generate its signal. A self-generating design does not require sensor excitation. For example, Metrix describes its 5485C as a moving-coil sensor requiring no external power. That example identifies a signal type; it does not establish compatibility with a CEZHEN sensor.

A piezoelectric velocity sensor uses a piezoelectric sensing element and electronic integration to produce a voltage proportional to vibration velocity. Its electronics require the specified powering arrangement. The YD33 manual describes internal integration and a constant-current supply. It should not be treated as a passive pickup.

Existing receiving arrangement	Replacement question
Input for a self-generating pickup	Can the channel support the proposed powered sensor, or is approved conditioning required?
Constant-current dynamic input	Do excitation, polarity, bias and signal swing match the exact sensor version?
4–20 mA process input	Is a configured overall transmitter output required rather than a dynamic velocity voltage?

Obtain the applicable terminal drawing before connecting equipment. A DC supply-voltage label alone does not specify a constant-current interface.

Read the complete sensitivity unit. Millivolts per inch per second and millivolts per millimetre per second differ by a factor of 25.4. As a unit-conversion example, 100 mV/(in/s) equals approximately 3.937 mV/(mm/s). It does not equal 100 mV/(mm/s). Use the exact calibration value for the selected sensor when configuring the receiver.

If a sensor already provides a dynamic velocity signal, configure the acquisition path for that quantity. Applying an acceleration-to-velocity integration setting to a velocity-proportional signal changes what is being measured. Confirm the receiver's input sensitivity, engineering units, filters and processing rather than copying another sensor's setup.

For an illustrative sensitivity of 3.94 mV/(mm/s), a sinusoidal velocity of 5 mm/s peak produces 19.7 mV peak within the applicable linear measurement band. This calculation is a scaling example, not a YD33 acceptance limit. RMS, peak and peak-to-peak conventions must still be recorded separately.

A dynamic voltage signal and a processed overall current value need different receiving paths. The 4–20 mA versus IEPE guide explains that distinction.

Specify the lowest and highest frequencies that matter to the task, together with the allowed amplitude error. A lower frequency printed without its tolerance is not enough to compare two sensors. For balancing or phase-based analysis, also request the phase response over the operating band.

Moving-coil pickups have a mechanical response associated with their suspended system. Piezoelectric velocity sensors have their own integration and filtering limits. Neither technology name establishes that a particular sensor can measure an arbitrarily low frequency.

Wilcoxon's technical notes, including Sensor selection considerations and Industrial vibration sensor selection: Piezovelocity transducers, discuss these response and phase differences. Their example frequency limits are not YD33 specifications. Compare the curves and tolerances for the actual proposed configuration.

Include operating-speed range and relevant vibration frequencies in the request. A machine's running speed helps identify frequencies of interest; it does not determine the complete required measurement band.

Keep the mounting arrangement, sensitive direction, cable and receiving input in the review. Confirm the thread, seating surface, available clearance and any adapter. Use the approved orientation and installation instructions for the selected pickup; a change of sensing technology does not approve an existing mount automatically. The mounting guide explains how attachment affects the measurement path.

For a powered dynamic sensor, also review cable length and capacitance, the available excitation and the input's coupling and voltage limits. A connector that fits does not establish its pin assignment, grounding or signal compatibility.

State sensor-surface and cable temperatures, moisture, chemical exposure and any hazardous-area requirements. Verify the applicable documentation for the complete supplied arrangement. An enclosure rating is not an explosion-protection approval, and another manufacturer's temperature or certification does not transfer to YD33.

The YD33 product is a piezoelectric vibration velocity sensor to review for a compatible powered dynamic input. The catalog reference and source comparison keeps its catalog values separate from the YD33 manual. The documents differ in range, sensitivity, temperature, protection and bias-voltage wording. Neither document identifies the currently supplied version.

The manual mentions replacement applications involving other manufacturers' products. That is not proof of a universal replacement or approval by those manufacturers. A useful review must match the actual sensor, monitoring channel and installation.

Provide the required configuration or existing component code. The reference's request checklist identifies the information needed without choosing unresolved values on your behalf.

You can begin with the details you have and mark the rest as unknown:

• Existing pickup's full model or order code and the receiving monitor or input-module model.
• Signal type, sensitivity with complete units, excitation and approved terminal or wiring diagram.
• Required vibration quantity, amplitude convention, frequency band and whether waveform, phase or only overall values are needed.
• Machine and measurement point, operating-speed range, mounting direction and mechanical drawing.
• Cable type and length, temperature and environmental or approval requirements.
• Reason for replacement, quantity required and any calibration record available for comparison.

Use Ask about this document below to keep this selection question attached to your request, or open the YD33 product for a model-specific inquiry. The review can identify missing information; it does not presume that a particular replacement is suitable.