Rockwell Automation 1746-NT8 SLC 500 Thermocouple/mV Analog Input Module User Manual - Manual (Page 50)

Publication 1746-UM022B-EN-P - January 2005
4-10 Channel Configuration, Data, and Status
For example, if channel one is configured as a thermocouple type
when the CJC breaks in an open-circuit condition, if open-circuit
detection is disabled, the data word remains unchanged. If the circuit
selection is set at minimum, the data word is set to the low scale value
for the range and format.
Select Temperature Units (Bit 9)
The temperature units bit lets you select temperature engineering
units for thermocouple and CJC input types. Units are either degrees
Celsius (°C) or degrees Fahrenheit (°F). This bit field is only active for
thermocouple and CJC input types. It is ignored when millivolt inputs
types are selected.
Select Channel Filter Frequency (Bits 10 and 11)
The channel filter frequency bit field lets you select one of four filters
available for a channel. The filter frequency affects the channel update
time and noise rejection characteristics. A smaller filter frequency
increases the channel update time, but also increases the noise
rejection and channel resolution. A larger filter frequency decreases
the noise rejection, but also decreases the channel update time and
channel resolution.
IMPORTANT
Enabling the open-circuit function adds
approximately 45 ms to the channel update time.
Disabling the open circuit detection removes the
time adder. CJC sensors do not require the additional
time; thus it is recommended that when using a
channel for CJC sensor acquisition, the open-circuit
selection is enabled.
IMPORTANT
If you are using engineering units (x1 mode) and
Fahrenheit temperature units (i.e. 0.1°F), the full
scale temperature for thermocouple type B is not
achievable with 16-bit signed numerical
representation. An over-range error occurs for that
channel if it tries to represent the full scale value.
The maximum representable temperature is 3276.7°F
(instead of 3308°F).