Chapter 3: Configuring the 2085-IT8-SC/IT-16-SC Using CCW
3-29
User’s Manual Pub. 0300322-01 Rev. A
Settings are:
Index
Open Circuit
Detection
Note
0
Upscale
Default
1
Downscale
2
Zero
3
Disable
6
*
Open circuit detection takes place on a periodic basis, every 4 seconds, by
temporarily enabling the PGA burnout current and initiating an ADC conversion
at the fastest filter frequency (470 Hz). This open circuit detection will also add
about 23 ms delay per channel on top of normal scan time.
The previous measurement remains in the input table during the open circuit
detection procedure (that is, the measurement value with the burnout current
enabled is not reported).
Within 3 seconds of an open circuit condition, transitional data may be reported
prior to the open circuit status bit being set.
Each channel has its own status bits to indicate open circuit fault in the input
table. Below are the cases for handling open circuit condition based on the Open
Circuit Detection selection,
•
For the Upscale option, the channel input reading will be set to the high
limit point based on the selected Input Type and Data Format. The
Channel Fault bit and the OC bit will be set.
•
For the Downscale option, the channel input reading will be set to the
low limit point based on the selected Input Type and Data Format. The
Channel Fault bit and the OC bit will be set.
•
For the Zero option, the channel input reading will be set to 0 no matter
what Input Type and Data Format is configured. The Channel Fault bit
and the OC bit will be set.
•
For the Disable option, an open circuit condition will not be reported.
Also, the periodic open circuit detection will not take place.
•
The Channel Fault bit and the OC bit will be cleared once the open
circuit condition on the channel has been resolved. The time to update
the bit status is controlled by the 4-second, or the module scan rate,
whichever takes longer.
•
If any limit value of the selected Input Type is beyond the signed 16-bit
Data Type limit, the data limit value will be assigned to the input channel
reading instead. This could happen when using Fahrenheit units with a
Type B or C thermocouple.
6
Disabling open circuit detection is available for all channels. When the measurement sensor is equipped with sensitive
low-impedance functionality, applying open circuit circuitry may affect the measurement accuracy. When the open
circuit detection is disabled, the corresponding open circuit status bit located in the channel status bits will not be
updated in the input table.
