Dwyer DPM - Manual (Page 32)

Particulate Monitoring Systems
Installation & Operating Manual
Document No. 210-1003-M Page 25 ©2007
Once the control unit and coaxial cable zero have been checked, proceed to the Sensor Zero Check.
To perform the sensor zero check the process flow must be stopped or a sensor test pipe (available
from Factory) or length of metal pipe will be needed (4”-6” diameter pipe or larger). The pipe should
be at least 3 in (8 cm) longer than the probe itself and must be grounded. The length of pipe will serve
as an electrical shield for the probe while it is out of the process.
SENSOR ZERO CHECK
1. Do not remove the sensor from a running process if it will in any way
compromise personnel, plant safety or hazardous area safety procedures.
2. Disconnect power to the control unit.
3. Remove the sensor from the process and insert it into the grounded metal
test pipe. For hazardous area sensors do not disconnect the external sensor
earth ground strap.
4. Re-apply power to the control unit and allow the reading to stabilize for 1-2
minutes.
5. Read the display. It should be below the control units specified minimum
detection level. If the sensor passes this check there are no false signals
from the sensor.
PASS:
1. Disconnect power to the control unit.
2. Remove the sensor from the grounded test pipe and re-insert into the
process. For hazardous area sensors do not disconnect the external sensor
ground strap.
FAIL:
1. Contact the factory for further assistance.
When performing a zero check, keep in mind that it may be acceptable to consider a small false signal
negligible. For example if the baseline readings are 100pA and a system zero offset of 1pA was
found, this is only a 1% affect on the normal readings. If using the device for basic flow/no flow
detection or basic emissions detection, this would not be significant.