Rotational Speed Sensors: Pulses, Low Speed and Outputs

A rotational speed sensor must work with the target wheel and the receiving input across the required speed range. Start with minimum and maximum shaft speed, the number of features detected per revolution, and whether the receiver needs a pulse signal or a processed speed value.

Measurement requirement	Configuration to review	Information needed
Passive magnetic pickup	Sensor, ferrous target and AC input	Signal amplitude at minimum speed and receiver threshold
Powered rectangular-wave sensor	Sensor supply and digital input	Output levels, load, target and frequency limits
Eddy-current speed signal	Probe, conditioner and compatible receiver	Complete system, target feature and input requirements
Speed value for a PLC or DCS	Sensor plus speed transmitter	Input selection, pulses per revolution and output scaling

These are different parts of a chain. A transmitter's 4–20 mA output does not mean its sensor input accepts a 4–20 mA signal. For CEZHEN options, review YD60, YD62 and YD240 with the application details below.

For a signal producing P complete pulses per mechanical revolution at n r/min, pulse frequency is f = n × P / 60, in hertz. Conversely, n = 60 × f / P. Count the events actually evaluated by the receiver: counting both edges or combining channels can differ from counting one pulse per tooth.

Speed	Pulses/revolution	Frequency
60 r/min	1	1 Hz
60 r/min	60	60 Hz
3000 r/min	1	50 Hz
3000 r/min	60	3000 Hz

For evenly spaced pulses, the interval is 1/f seconds. At 60 r/min, the first two examples give intervals of 1 s and about 16.7 ms. At 3000 r/min, the intervals are 20 ms and about 0.333 ms.

These are arithmetic examples, not tested operating points or approved CEZHEN configurations. More teeth increase frequency at the same shaft speed. Check the maximum frequency of the sensor, transmitter and receiving input; also ask about minimum pulse width, filters and the receiver's counting convention. A nominal rpm range alone cannot answer those questions.

At low speed, fewer pulses also mean a longer wait between events. State the required update time and how quickly a stopped shaft must be recognized. The receiver's measurement method and timeout need confirmation.

A passive variable-reluctance pickup generates an AC signal as a suitable target moves past it. Honeywell's VRS explanation describes how signal amplitude and frequency vary with movement. Its industrial application guidance also treats target geometry, air gap and loading as application conditions. This general principle does not provide a universal minimum rpm or mounting gap for another sensor.

The YD60 catalog reference lists at least 300 mV at 50 r/min and a separate frequency-response entry above 30 Hz. The listed amplitude does not identify the complete test target, gap, load or whether the value is peak, peak-to-peak or RMS. Do not convert either entry into a guaranteed minimum shaft speed for every tooth count.

Ask for the minimum signal at the proposed target and gap, then compare it with the receiver's input threshold using the same amplitude definition. A shared number such as 300 mV is insufficient to establish input margin or compatibility. Include startup and coastdown requirements in that review.

A powered magnetic speed sensor is a different electrical arrangement from a passive pickup. Hall-effect and other powered sensing designs may provide digital output; the specific design determines its low-speed behavior. Honeywell's LCZ series is one documented Hall-effect zero-speed example. That capability is specific to the stated product, not proof that every powered sensor and receiver can detect standstill in the same way.

The YD62 reference lists a powered rectangular-wave output. Review its supply, high and low levels, output load and target-material conditions against the intended input. Its 0–20 kHz catalog entry does not establish the response time of a complete stopped-shaft alarm. A stationary target produces no sequence of passing teeth; the receiving system must apply its defined interpretation.

For hazardous-area use, request the applicable documentation for the exact supplied configuration and installation. A catalog marking alone does not establish project approval.

For an AC pickup input, obtain the accepted amplitude range, amplitude convention, frequency band, impedance and threshold settings. For a powered digital input, confirm signal levels, common reference, loading and required output circuit. Use the approved terminal drawing for the supplied equipment.

YD240's catalog ordering table separately identifies input-sensor selection, pulses per revolution, speed range and output. It lists 4–20 mA or RS-485 as output choices. For a current-output request, specify the desired speed at 4 mA and at 20 mA, the receiving load and supply. For serial integration, request the applicable protocol and register information; RS-485 names an electrical interface and does not by itself identify the available data.

The monitoring instrument reference describes speed and direction-monitoring arrangements separately. Do not assume that one speed pulse train establishes direction detection, or that a speed transmitter supplies a phase-reference signal for vibration analysis. State those tasks explicitly if required.

Published CEZHEN descriptions of YD240 differ. The catalog reference lists an AC input greater than 300 mV without an amplitude convention. A separate three-page company sheet states an input greater than 2 V peak-to-peak and describes additional settings. These are not equivalent acceptance conditions.

The sources also print different frequency endpoints and enclosure dimensions. The unit at the lower frequency endpoint is not established clearly enough to infer a low-speed limit. See the YD240 configuration comparison before selecting from those descriptions.

Provide the full model code, nameplate and available drawing or manual for an existing unit. For a new installation, ask which configuration and input specification will be supplied. Do not combine one source's input sensitivity with another source's features.

Include the following details in your first request. Unknown items can remain unknown.

• Machine, measurement point, minimum and maximum speed, including startup or coastdown needs.
• Target material, wheel diameter, tooth or feature count, geometry and available mounting space.
• Sensor model, supply and output; proposed gap and cable length if known.
• Receiver or transmitter model, input specification and counted pulses per revolution.
• Required speed output, current scaling or serial integration information, and update or stopped-shaft response time.
• Temperature, installation conditions, quantity and any required hazardous-area documentation.

For a replacement, include the complete existing sensor and transmitter codes rather than only the connector or thread size. Use Ask about this document below to retain this selection context, or open a product above for a model-specific request. The initial message remains editable so you can describe the actual task.