Spectrum Controls Micro800 2085-IR8-SC User Manual page 49

Chapter 3: Configuring the Micro800 Expansion I/O 2085-IR8-SC Using CCW
detected, but it takes 6 to 10 seconds to detect that the excitation wire is
reconnected.
•
3-wire lead resistance is measured at 60-seconds intervals; 3-wire lead
open circuit is also detected once every 60 seconds.
•
3-wire lead resistance needs the following conditions present to be
measured at a faster rate than once every 6 seconds. These conditions are
not considered normal conditions. Once any of these conditions is
removed, lead wire returns to being measured at the rate of once every 60
seconds.
•
In 4-wire mode, open circuit detection takes place on a periodic basis,
every 5 seconds, alternating between the primary wire pair and the
secondary wire pair, by temporarily enabling the PGA burnout current
and initiating an ADC conversion at the fastest filter frequency (470 Hz).
This open circuit detection also adds about 23 ms delay per channel, on
top of normal scan time. If all channels are configured as 4-wire mode
and enabled, there will be an additional 184 ms scan time added for open
circuit detection once every 5 seconds. Depending on the filter setting,
any open wire in 4-wire mode is detected within 5 to 15 seconds.
•
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 the period of an open circuit condition, transitional data may be
reported before the open circuit status bit is set.
Each channel has its own status bits to indicate open circuit fault in the input
table. Below are the cases on handling open circuit condition based on the Open
Circuit Detection selection:
•
For the Upscale option, the channel input reading is set to the high limit
point based on the selected Input Type and Data Format. The Channel
Fault bit and the OC bit are set.
•
For the Downscale option, the channel input reading is set to the low
limit point based on the selected Input Type and Data Format. The
Channel Fault bit and the OC bit are set.
•
For the Zero option, the channel input reading is set to 0 no matter what
Input Type and Data Format is configured. The Channel Fault bit and the
OC bit are set.
-
When any channel has the lead wire open, and open circuit
detection is enabled, lead wire is measured once every 6 seconds
until there is no longer an open wire on any of the channels.
-
If a previous lead wire measurement and the current lead wire
measurement difference is more than 0.5 ohms, the lead wire is
measured once every 6 seconds until the read difference between
the two is less than 0.5 ohms.
-
If measured lead wire resistance is larger than 25 ohms, lead
wire is measured once every 6 seconds until it is less than 25
ohms.
-
In the above cases, it takes about 6 to 10 seconds to detect the
lead wire open or to recover.
User's Manual Pub. 0300321-01 Rev. A
3-25