Ametek Thermox TM2000, User Manual

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Controller / User Interface | 4-13
Primary Calibration
The actual furnace temperature set point will vary from unit-to-unit based
upon the Primary Calibration which correlates the actual cell response
for the desired 615°C cell set point temperature with the actual furnace
thermocouple feed back temperature. This is accomplished by applying
two known concentrations of oxygen to the analyzer during the primary
calibration. The software algorithm then calculates the actual cell tempera-
ture from the cell mV response and then makes the appropriate increase
or decrease in the furnace temperature control set point. If you take the
displayed cell temperature and divide it by the T/C Ratio in memory loca-
tion 88, then this is the actual furnace set point control temperature. If you
take a Type-K table, you should be able to measure the voltage on termi-
nals C and D on the sensor board, and then add the appropriate amount
of mVs for the board ambient, your corresponding temperature from a
Type-K thermocouple should be the actual furnace set point temperature
= 615°C / T/C Ratio (memory location 88).
Use the Type-K table to determine the mV change you have for 273°C and
adding this mV change for the actual board temperature, should be the
compensation voltage measured between D+ and 6- on the sensor board.
So for a 50°C ambient at the board, the voltage should be 11.05 mV (273°C)
+ 2.02 mV (50°C) = 13.07 mVs.
If you have a T/C ratio of 0.9, the corresponding furnace temperature
set point should be (615°C / 0.9 = 683°C). If you measure the voltage at
terminals C and D on the sensor board with a 50°C ambient, the voltage
should be 28.414 (683°C) - 2.02 mV (50°C) = 26.4 mV. If you add in the
compensation voltage for 50°C, the voltage at terminals 5 and 6 should be
26.4 mV + 12.05 mV = 38.44 mVs which should also be the voltage that
you measures at T/C+ and T/C - terminals on the Series 2000 wiring card
terminals and also the displayed T/C mV value that you can set one of the
display lines to view in the Setup key - Display menu.
Based upon the age of your cell and its characteristics, the control temper-
atures should be slightly different. However if you incorrectly perform a
primary calibration or if the cell really starts to deteriorate, the actual cell
response to calibration gas will drop off. The primary calibration is a why
to extend the life of the cell since the furnace control temperature can be
increased as the cell ages to reduce the atrophy and extend the cell life
if the output starts to drop off at its original factory cal furnace set point
temperature. You can tell this with the distribution that you have in your
spreadsheet since the calculated cell temperatures for some of the analyz-
ers are well below 615°C or above by a fair amount. If the cell response
goes out of the following limits, you will receive a zero or span gas range
error. At this point, you should perform a primary calibration and then
attempt a standard calibration again. If you get an excess cal error during