Rockwell Automation 1769-IT6 Compact I/O 1769-IT6 Thermocouple/mV Input Module - Manual (Page 45)

Rockwell Automation Publication 1769-UM004B-EN-P - March 2010 45
Module Data, Status, and Channel Configuration Chapter 4
Scaled-for-PID
The value presented to the controller is a signed integer, with 0 representing the
lower input range and 16,383 representing the upper input range.
To obtain the value, the module scales the input signal range to 0…16,383, which
is standard to the PID algorithm for the MicroLogix 1500 controller and other
Allen-Bradley controllers (for example, SLC controllers). For example, if a type J
thermocouple is used, the lowest temperature for the thermocouple is -210 °C
(-346 °F), which corresponds to 0 counts. The highest temperature in the input
range, 1200 °C (2192 °F), corresponds to 16,383 counts.
Percent Range
Input data is presented as a percentage of the specified range. The module scales
the input signal range to 0…10,000. For example, using a type J thermocouple,
the range -210…1200 °C (-346…2192 °F) is represented as 0…100%.
See
Determining Effective Resolution and Range on page 50.
Selecting Input Type (bits 11…8)
Bits 11…8 in the channel configuration word indicate the type of thermocouple
or millivolt input device. Each channel can be individually configured for any
type of input.
Selecting Temperature Units (bit 7)
The module supports two different linearized/scaled ranges for thermocouples,
degrees Celsius (°C) and degrees Fahrenheit (°F). Bit 7 is ignored for millivolt
input types, or when raw/proportional, scaled-for-PID, or percent data formats
are used.
IMPORTANT If you are using engineering units x 1 data format and degrees Fahrenheit
temperature units, thermocouple types B and C cannot achieve full-scale
temperature with 16-bit signed numerical representation. An over-range
error will occur for the configured channel if it tries to represent the
full-scale value. The maximum representable temperature is 1802.61 °C
(3276.7 °F).