Allen-Bradley Compact 1769-IR6, User Manual

Page: 54 / 116

Publication 1769-UM005A-EN-P
4-14 Module Data, Status, and Channel Configuration
Selecting Temperature Units/Mode (Bit 7)
The module supports two different linearized, scaled temperature ranges
for RTDs, degrees Celsius (°C) and degrees Fahrenheit (°F). You can
select the type that is appropriate for your application by setting bit 7 in
the channel configuration word. Bit 7 is ignored for resistance input types
or when raw/proportional, scaled-for-PID, or percent data formats are
used.
Selecting Open-Circuit Response (Bits 5 and 6)
Broken inputs for the module include open-circuit and short-circuit
conditions. An open-circuit occurs when the module’s maximum input
voltage is reached. This can happen if the wire is cut or disconnected
from the terminal block. The module can encounter an open-circuit for
any RTD or resistance input.
A short-circuit occurs when the calculated lead wire compensated
resistance is less than 3
Ω
. The module can only report a short-circuit for
an RTD.
Use bits 5 and 6 of channel configuration word 6 to define the state of the
channel data word when a broken input condition is detected for the
corresponding channel. When it detects an open circuit or a short circuit,
the module overrides the actual input data with the value that you specify.
Selecting Cyclic Lead Compensation (Bit 4)
For each channel, the module measures lead resistance in one of two
ways. Set bit 4 to 0 to
enable measurement and compensation of lead
resistance every five minutes. One channel is measured per module
update to limit the impact to channel throughput. You can also implement
a lead wire calibration cycle any time, at your command, by enabling and
then disabling this bit in your control program.
(1)
Regardless of the state
of bit 4, lead wire compensation occurs automatically on a system mode
Table 4.6 Open/Broken Circuit Response Definitions
Open/Broken
Circuit Value Response Definition
Upscale Sets input to full upper scale value of channel data word. The full-scale
value is determined by the selected input type, data format, and scaling.
Downscale Sets input to full lower scale value of channel data word. The low scale
value is determined by the selected input type, data format, and scaling.
Last State Sets input to last input value.
Zero Sets input to 0 to force the channel data word to 0.
(1) Not all controllers allow online configuration changes. Refer to your controller’s user manual for details. During an
online configuration change, input data for that channel is not updated by the module.