- PCME STACK 990 MANUAL: 71 -
11.8 Sensor Reading too Low or too High
The controller gets the reading from the sensor using digital modbus communication which has
error checking. Therefore if a reading is being displayed at the control unit without any “No
Response” message (and not frozen – see section above) you can be confident this is a genuine
reading from the sensor. If it is not the reading you expect consider the following:
• Adjust the sensor sensitivity (go to the More Settings menu).
• Adjust the calibration factor: dust monitors do not provide a reading pre-calibrated to
mg/m
3
. To scale the Sensor reading adjust the Calibration Factor (go to Sensor Settings).
• Check the grounding of the sensor. For electrodynamic sensors it is essential the sensor
body is grounded to the stack. Poorly grounded sensors may pick up external noise
producing false high readings.
If you are using an earthing strap ensure this is firmly attached to the stack.
If you are not using an earthing strap the sensor relies on the thread or flange connection to
provide grounding:
• Remove any PTFE tape from the thread
• Remove rust from the thread and apply copper slip or grease
If the stack if not metallic or you are concerned the stack may not provide a suitably earthed
shield for the sensor then contact PCME.
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