- PCME STACK 990 MANUAL: 56 -
7.2 PCME STACK 990 Sensor Self Tests
The QA screen allows the status of the hardware self-checks to be reviewed for each sensor.
These may be set to run automatically and can also be manually forced (i.e. during installation or
maintenance).
Self Tests provide automatic monitoring of the integrity of sensors. The Controller can be
configured to provide alarm notification of self test failures. In addition self tests can be manually
run to check the validity of measurements before carrying out isokinetic sampling used for
calibration.
The main self tests provided are:
Contamination Checks (Short Circuit, Contamination Ring): indicate the probe needs cleaning.
Zero and Span Checks: used to check for faults with the sensor hardware.
The main display on the QA screen displays various Self Check Results for the currently selected
sensor. The choice of sensor is made from the edit box at the top of the main display. For each
test the display alternates between PASS or FAIL and a numerical result of the test: the meaning
of these numbers is explained below.
Zero check and Span Checks
These are used to test the correct functioning of the sensor. The QA screen shows Zero and Span
check results for the Main Probe (used for measurement). Failure of these tests suggests the
sensor may be physically damaged in some way.
Short Circuit Check
The short circuit check performs a basic test for contamination between the probe rod and the
base of the probe by checking for the existence of an electrical short circuit.
Contamination Ring Check
The contamination ring check performs a more advanced check for contamination interference on
the probe measurement. The contamination ring check runs continuously during normal
operation. The result displayed is a measure of the triboelectric signal measured on the
contamination ring at the base of the probe. This signal is compared to the signal measured on
the main measurement. If this level is large (as a percentage) it indicates a possible
contamination interference problem. If either the Short circuit Check or Contamination Ring Test
fails it suggests the sensor needs cleaning and may not be providing reliable measurements.
Self Test Values
The following table gives the numerical values required for the self tests to pass:
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