Spectrum Controls 1769sc-IF8u - Manual (Page 55)

Chapter 4: Module Data, Status, and Configuration 45
Selecting Input Type (Bits 10 through 6)
Bits 10 through 6 in the channel configuration word indicate the type of
input device. If channels 1, 3, 5, or 7 are configured for RTD or
Resistance type, the configuration for the following even channels (2, 4, 6,
8) are ignored, respectively. It is recommended to set both channels
identically (1 and 2, 3 and 4, 5 and 6, or 7 and 8) when setting a channel to
RTD or Resistance mode. This reduces confusion in the setup. A zero
will be reported, in the input data word, for the respective even channel in
RTD mode to reflect the RTD or resistance mode configuration. The 4-
20 mA range is the default input type for each channel.
Note: The on-board jumpers must be changed to voltage mode if any
other input type is desired other than current.
Determining Open-Circuit Response (Bits 5 and 4)
An open-circuit condition occurs when an input device or its extension
wire is physically separated or open. This can happen if the wire is cut or
disconnected from the terminal block.
NOTE: If the CJC sensor is removed from the module terminal block, its
open-circuit bit is set (1) and the module continues to calculate
thermocouple readings at reduced accuracy. If an open CJC circuit is
detected, the module uses 25°C as the sensed temperature at that location.
Channels that are configured for other input types are not affected by CJC
open-circuit conditions. See Open-Circuit Detection in chapter 5 for
additional details.
Bits 5 and 4 define the state of the channel data word when an open-
circuit or short circuit condition is detected for the corresponding channel.
The module overrides the actual input data depending on the option that
you specify when it detects an open circuit. The open-circuit options are
explained in the table below.
Response Option Definition
Upscale
Sets the input data value to full upper scale value of channel data
word. The full-scale value is determined by the selected input type and
data format.
Downscale Sets the input data value to full lower scale value of channel data word.
The low scale value is determined by the selected input type and data
format.
Last State Sets the input data value to the last input value prior to the detection of
the open-circuit.
Zero 1 Sets the input data value to 0 to force the channel data word to 0.
1
If 0 is out-of-range for the selected input type, the data value w ill default to minmum scale on open circuit.