ROC364 Instruction Manual
3-22
Input and Output Modules
Rev Jun/05
3.5.1 Analog Input Modules
Equipment Required:
Multimeter
To determine if an Analog Input module is operating properly, its configuration must first be known.
Table 3-2 shows typical configuration values for an Analog Input:
Table 3-2. Analog Input Module Typical Configuration Values
Parameter Value
Corresponds
To
Adjusted A/D 0 %
800
1 volt dc across scaling resistor R
s
Adjusted A/D 100 %
4000
5 volts dc across R
s
Low Reading EU
0.0000
EU value with 1 volt dc across R
s
High Reading EU
100.0
EU value with 5 volts dc across R
s
Filter EUs
xxxxx
Value read by AI module
When the value of Filtered Engineering Units (EU) is –25% of span as configured above, it is an
indication of no current flow (0 milliamps), which can result from open field wiring or a faulty field
device.
When the value of Filtered EUs is in excess of 100% of span as configured above, it is an indication of
maximum current flow, which can result from shorted field wiring or a faulty field device.
When the value of Filtered EUs is between the low and high readings, you can verify the accuracy of the
reading by measuring the voltage across scaling resistor R
s
(V
rs
) with the multimeter. To convert this
reading to the filtered EUs value, perform the following:
Filtered EUs = [((V
rs
– 1)
÷
4)
×
Span] + Low Reading EU,
where Span = High Reading EU – Low Reading EU
This calculated value should be within one-tenth of one percent of the Filtered EUs value measured by
the ROC. To verify an accuracy of 0.1 percent, read the loop current with a multimeter connected in
series with current loop. Be sure to take into account that input values can change rapidly, which can
cause a greater error between the measured value and the calculated value.
If the calculated value and the measured value are the same, the AI module is operating correctly.
3.5.2 Analog Output Modules
The Analog Output module is a source for current loop or voltage devices. Two test procedures are
provided to verify correct operation.
♦
Check AO Current Loop Source Installations on page 3-23.
♦
Check AO Voltage Source Installations on page 3-23.