PROBE BUDDY – USER MANUAL
Page 11 of 27
UPC_MAN013_R7
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Probe Test Mode
The probe impedance test is performed by measuring the voltage of the probe, applying a
known shunt resistor across it, and then measuring the shunted voltage output. The value of
the shunt resistor is 10kohm for oxygen sensors.
To run a probe impedance test it is necessary to setup the probe testing parameter in the
SETUP Probe Menu, and the PROBE BUDDY is configured for signal inputs. Please refer to
Probe parameters table for an explanation of these setup parameters. You may choose to
accept the defaults for the other parameters in this menu or change them to suit your
applications. It is necessary that the sensor be above the MIN PROBE TEMP parameter
setting for this test to run. It is also necessary for the probe to measure a stable process gas
during this test. To start the test,
press the ENTER and ► keys at the same time.
The test can
be stopped by pressing the ENTER and ► keys again.
The following table explains the operations of the impedance test. The PROBE BUDDY will
display the averaging time countdown and the results.
Sequence #
Description
1
Inhibit process variable calculations
Freeze alarms at last state except
clear any previous probe test failure
alarm
Store present probe millivolt reading
Apply shunt resistor across probe
2
Wait for impedance test timer, fixed
time of 30 seconds
Compute impedance of probe and
remove shunt resistor. Save measured
impedance as PROBE IMPEDANCE in
INFO menu.
If impedance is greater than PROBE
IMP LIMIT, then set probe test failure
alarm.
3
Wait for probe to recover to >=99% of
original millivolts
Evaluate actual recovery time to IMP
RECVRY TIME
If recovery time is greater than IMP
RECVRY TIME, then set probe test
failure alarm.
Store recovery time (or max value) as
IMP RECVRY TIME in INFO menu
1.8.1 Why Measure Sensor Impedance?
