PROBE BUDDY – USER MANUAL
Page 12 of 27
UPC_MAN013_R7
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All rights to copy, reproduce and transmit are reserved.
It is important to track sensor impedance over a period of time to help determine the
replacement schedule for the sensor. A high impedance (>50 K
Ω
) indicates that the electrode
contact on the probe zirconia is deteriorating to a level that probably warrants replacement.
High sensor impedance results in a lower signal output from the sensor and an eventual failure
of the electrode connection on the process side of the zirconia ceramic. This deterioration is
more of a factor in highly reducing atmospheres. In such applications, it may be necessary to
check the impedance at least once a month. Under light reducing, annealing, or brazing
operations, the impedance may not have to be checked unless there is a question about the
probe’s performance.
A typical impedance for a new probe is less than 1 K
Ω
. As the probe starts to age, the
impedance will increase. Past 20 KOHM the sensor should be monitored more closely. Above
50 K
Ω
, the sensor should be replaced. If it is necessary to replace the sensor, remove it
carefully following the instructions supplied with the sensor. Do not discard a sensor with a
high impedance. It may be possible to rebuild the sensor if the ceramic parts are intact.
Contact United Process Controls for information on rebuilding your sensor.
An impedance test can only be performed if the probe temperature is at or above 1100°F
(600°C) with a stable atmosphere present.
A 10K
Ω
resistor is shunted across the sensor output. The sensor impedance is calculated as:
Rx = [(Eo/Es)-1]*Rs
Where Rx = sensor impedance, Eo = sensor’s open circuit voltage, Es = shunted sensor’s
voltage, and Rs = shunt resistor. The units of Rx are the same as Rs.
The Sensor test process screen is displayed while a test is
running.
If the Enter/► dual keys are pressed while the
PROBE BUDDY is
configured for inputs, the display will momentarily display the message - CHANGE TO
OUTPUT MODE.
Alarm Display
Alarm display alerts the operator about a fault in the PROBE BUDDY or signals exceeding the
limits of the inputs.
A major fault or alarm screen must be acknowledged using the
Enter key. System fault alarms will reoccur if the fault continues.
High value displays when the signal exceeds the display or
maximum limit of the signal input.
Probe Test
Recovery Time
ALARM
FLASH CSUM
HHHH°C 0.00%
72.0mV %O2
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