OMRON Z4M sensor precision measurement

4.2 Balancing Response Time and Resolution

The response time selector provides three levels (for Z4M-W40: 0.15ms/2ms/60ms; For Z4M-W100: 0.7ms/20ms/500ms. Its essence is the cut-off frequency setting of the internal low-pass filter: the stronger the filtering, the better the noise suppression (higher resolution), but the slower the response. Engineers should judge based on the target movement speed: if the frequency of target displacement change is f, the response time should be at least less than 1/(2f). For example, detecting 100Hz vibration requires a response time of ≤ 5 milliseconds. In this case, the Z4M-W40 should choose the 2ms range (resolution of 10 μ m), while the Z4M-W100 has a minimum of only 0.7ms (but resolution of only 150 μ m), which is more suitable for low-frequency large displacement measurement.

When evaluating response time, it should be noted that the values given in the data manual are 10% to 90% rise/fall time. If the output is required to be stable within the 1% error band of the final value, it actually requires 2-3 times the nominal response time. For example, in the 60ms gear, stabilizing to 1% accuracy takes approximately 120-180ms.

Offset and range calibration methods

5.1 Offset Adjustment

The default calibration conditions at the factory are: the white alumina ceramic target is located at the measurement center point (40mm or 100mm), with a linear output of 0V. In practical applications, the target material may be different from the white ceramic, resulting in zero point offset. The offset adjustment steps are as follows:

Accurately fix the target at the desired measurement zero position (usually the reference plane of mechanical motion).

Use a precision voltmeter to monitor the linear output voltage.

Rotate the offset adjuster on the amplifier with a small screwdriver to reset the output voltage to zero (0V ± acceptable deviation).

The effective range of offset adjustment is ± 10mm (for Z4M-W40) or ± 40mm (for Z4M-W100), and the output voltage can be adjusted to within ± 5V range. Beyond this range, linearity cannot be guaranteed.

5.2 Span Adjustment

Range adjustment changes the sensitivity coefficient of output voltage to distance variation. The factory default values are 0.4 V/mm (Z4M-W40) and 0.1 V/mm (Z4M-W100), corresponding to 8V output when the full range changes by 20mm or 80mm. In practical applications, if one wishes to amplify displacement signals with small amplitudes, the range setting value can be increased. Calibration steps:

After completing the offset adjustment, move the target from zero by a known distance Δ d (e.g. 5mm).

Measure the output voltage change Δ V at this time.

Rotate the range adjuster to achieve the desired value of Δ V/Δ d. Note that the range adjustment range is ± 30% of the default value, which means that the sensitivity of Z4M-W40 can be adjusted between 0.28~0.52 V/mm.

Re verify the zero offset, as range adjustment may slightly affect the zero point - iterate calibration if necessary.

A typical application scenario: It is necessary to expand the ± 4V output to ± 5V to match a higher ADC input range. The operation method is: first move the target to the position where the output is 4V, then adjust the range regulator to raise the voltage to 5V. At this time, the voltage output corresponding to the full range distance becomes ± 5V, but the linearity index remains.

Status indication and fault diagnosis

6.1 Meaning of indicator light combination

Both the sensor body and amplifier have NEAR and FAR indicator lights, and the amplifier also has a separate stability indicator light (green/red/off).

Meaning and handling measures of NEAR FAR stability indicator light

The bright green target is within the effective measurement range, with sufficient received light and stable measurement. This is the ideal working state.

Bright and extinguished the target within the range, but the amount of received light is in the critical zone (possibly due to low target reflectivity). Check the sensitivity switch settings and try switching from WHITE to BLACK or AUTO.

Turning on or off the red color, or turning off the target if the distance is too close (less than the near end limit of the sensor), or if the reflected light is too strong (such as a mirror). Move the target away or reduce surface reflection.

Turn off the red light or turn off the target too far away (beyond the far end limit), or the reflected light is extremely weak. Move closer to the target or check for light path obstruction.

Flashing red with no target or abnormal extreme light intensity. Confirm that the laser is turned on (laser OFF input open circuit, and power on preheating period has expired).

6.2 Common abnormal phenomena and their elimination

Phenomenon 1: The output voltage remains between 6~8V and does not vary with distance.

Possible reason: Enable output OFF, meaning the sensor has not recognized valid measurements. Check: Is the target within the measurement range? Is the laser turned on (observe if the NEAR/FAR indicator lights are on or flashing)? Does the sensitivity switch match the target reflectivity?

Phenomenon 2: The stability indicator light is green, but the output noise is high.