Rockwell Automation 1746-NT8 SLC 500 Thermocouple/mV Analog Input Module User Manual - Manual (Page 45)

Publication 1746-UM022B-EN-P - January 2005
Channel Configuration, Data, and Status 4-5
Select Channel Enable (Bit 0)
Use the channel enable bit to enable a channel. The thermocouple
module only scans enabled channels. To optimize module operation
and minimize throughput times, unused channels should be disabled
by setting the channel enable bit to zero (default value).
When set (1) the channel enable bit is used by the module to read the
configuration word information selected. While the enable bit is set,
modification of the configuration word may lengthen the module
update time for one cycle. If any change is made to the configuration
word, the change is reflected in the status word before new data is
valid (described on page 4-11).
While the channel enable bit is cleared (0), the associated channel
data/status word values are cleared. After the channel enable bit is set
(1), the associated channel data/status word remains cleared until the
thermocouple module sets the channel status bit (bit 0) in the channel
status word.
Select Input Types (Bits 1 through 4)
The input type bit field lets you configure the channel for the type of
input device you have connected to the module. Valid input devices
are types J, K, T, E, R, S, B, and N thermocouple sensors and ±50 mV
and ±100 mV analog input signals. The channel can also be
configured to read the cold-junction temperature calculated for that
specific channel. When the cold-junction compensation (CJC)
temperature is selected, the channel ignores the physical input signal.
Select Data Format (Bits 5 and 6)
The data format bit field lets you define the expressed format for the
channel data word contained in the module input image. The data
types are engineering units, scaled-for-PID, and proportional counts.
The engineering units allow you to select from two resolutions, x1
or x10. For engineering units x1, values are expressed in 0.1 degrees
or 0.01 mV. For engineering units x10, values are expressed in 1.0
degrees or 0.1 mV. (Use the x10 setting to produce temperature
readings in whole degrees Celsius or Fahrenheit.)
The scaled-for-PID value is the same for millivolt, thermocouple, and
CJC input types. The input signal range is proportional to your
selected input type and scaled into a 0 through 16,383 range, which is
standard to the SLC PID algorithm.