Rockwell Automation 1762-IR4 RTD/Resistance Input Module - Manual (Page 38)

Publication 1762-UM003A-EN-P - February 2003
3-4 Module Data, Status, and Channel Configuration
Input Data Not Valid Condition
The general status bits S0 to S3 also indicate whether or not the input
data for a particular channel, 0 through 3, is being properly converted
(valid) by the module. This “invalid data” condition can occur (bit set)
when the download of a new configuration to a channel is accepted
by the module (proper configuration) but before the A/D converter
can provide valid (properly configured) data to the MicroLogix 1200
controller. The following information highlights the bit operation of
the Data Not Valid condition.
1. The default and module power-up bit condition is reset (0).
2. The bit condition is set (1) when a new configuration is received
and determined valid by the module. The set (1) bit condition
remains until the module begins converting analog data for the
previously accepted configuration. When conversion is
complete, the bit condition is reset (0) by the module. The
amount of time it takes for the module to begin the conversion
process depends on the number of channels being configured
and the amount of configuration data downloaded by the
controller.
3. If A/D hardware errors prevent the conversion process from
taking place, the bit condition is set (1).
Open-Circuit Flag Bits (OC0 to OC3)
Bits OC0 through OC3 of word 4 contain open-circuit error
information for channels 0 through 3, respectively. For an RTD input,
the bits indicate either an open-circuit or short-circuit condition when
set (1). For a resistance input, the bits indicate an open-circuit when
set (1).
TIP
If the new configuration is invalid, the bit
function remains reset (0) and the module posts
a configuration error. See Configuration Errors
on page 4-6.
TIP
Short-circuit detection for direct resistance inputs is
not indicated because 0 is a valid number.