Chapter 3: Configuring the 2085-IT8-SC/IT-16-SC Using CCW
3-25
User’s Manual Pub. 0300322-01 Rev. A
The
scaling formula
with the channel bias applied is:
𝑦 = 𝑚𝑥 + 𝑏 + 𝐶ℎ𝑎𝑛𝑛𝑒𝑙 𝐵𝑖𝑎𝑠
Where:
𝑦
is the final scaled reading shown in the input table
𝑚
is the gain:
𝑚 =
(𝑈𝑠𝑒𝑟 𝐻𝑖𝑔ℎ 𝐿𝑖𝑚𝑖𝑡 − 𝑈𝑠𝑒𝑟 𝐿𝑜𝑤 𝐿𝑖𝑚𝑖𝑡)
(𝐴𝑐𝑡𝑢𝑎𝑙 𝐻𝑖𝑔ℎ 𝐿𝑖𝑚𝑖𝑡 − 𝐴𝑐𝑡𝑢𝑎𝑙 𝐿𝑜𝑤 𝐿𝑖𝑚𝑖𝑡)
The User High/Low Limit value is based on the selected Input Type and the
selected Data Format. The Actual High/Low Limit value is the actual limits of
the selected Input Type without scaling. See table above.
For example, if Type B Thermocouple and EU×1 are selected in the
configuration table, the gain will be 10 = (18200-3000) / (1820-300), m = 10.
𝑥
is the ADC signal data acquired at the terminal block and converted to the
corresponding data format.
For a Thermocouple input, this
𝑥
is the actual temperature in °C. The circuit
board first reads in the ADC data count. Data count is then converted to
millivolts based on the gain setting of the ADC. Next the millivolt reading is
converted to temperature in °C based on the thermocouple curve specification.
𝑏
is the offset:
𝑈𝑠𝑒𝑟 𝐿𝑜𝑤 𝐿𝑖𝑚𝑖𝑡 − (𝑚 ∗ 𝐴𝑐𝑡𝑢𝑎𝑙 𝐿𝑜𝑤 𝐿𝑖𝑚𝑖𝑡)
.
In above example,
𝑏
= 3000 – (10 * 300) = 0, so if the thermocouple measured
10.0 degrees C, then the display of the reading for EU×1 is 10.0 * 10 + 0 +
Channel Bias.
𝐶ℎ𝑎𝑛𝑛𝑒𝑙 𝐵𝑖𝑎𝑠
is an offset in integer format.
The Channel Bias value is only applied to the raw measured value. It will not be
applied to shift the minimum and the maximum points and the limits of the
selected Input Type range. If the final channel input reading is equal to, or goes
beyond, the minimum or the maximum point of the selected Input Type range,
Channel Fault and an Over/Under Range Fault bits will be set in the input table.
The other case is, if the final input reading reaches the Data Type limit (-32768
or +32767) before reaching the minimum or the maximum point of the selected
Input Type range, the same Fault bits will be set in the input table.
3.6.5
Channel Temperature Unit
The module provides a feature to select the temperature display unit for each
channel input reading if the channel is configured to use thermocouple
measurement with EU×1 or EU×10 Data Format used.
Index
Unit
Note
0
ºC
Default
1
ºF
