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ROC364 Instruction Manual

Rev 5/00 6-11

6.5.1 Analog Input Channels

Equipment Required: Multimeter

To determine if an Analog Input channel is operating properly, its configuration must first be known.

Table Section: 6-1 shows typical configuration values for an analog input:

Table Section: 6-1. Analog Input Channel Typical Configuration Values

PARAMETER VALUE CORRESPONDS TO:

Adj. A/D 0 % 800 1 volt dc across R

(scaling resistor R1)

Adj. A/D 100 % 4000 5 volts dc across R

Low Reading EU 0.0000 EU value with 1 volt dc across R

High Reading EU 100.0 EU value with 5 volts dc across R

Filtered EUs xxxxx Value read by AI channel

When the value of Filtered Engineering Units (EU) is -25% of span as configured above, it is an

indication of no current flow (0 mA), 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

) with the multimeter. To convert

this reading to the Filtered EUs value, perform the following:

Filtered EUs = [((V

- 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 channel is operating correctly.

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