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Analog Signal Input

Verbatim Owner's Manual B-11

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B.1.9 If Analog Inputs Do Not Work Correctly

Recheck programming settings, especially the Input Signal Type setting. Verify

that the polarity of your input connections is correct.

In the case of 4-20 ma input, does the spoken value always reflect a 0 ma signal

level? If so, the problem is presumably with the connection or the signal source.

Use a DC meter to verify that both sides of the offending input are within 10

VDC of ground. A 4-20 ma current loop input should give a meter reading of

about .07 volt per milliamp of current as measured across the two signal input

terminals.

Are other instruments included in the same current loop? If they read correctly,

temporarily disconnect the input to the Verbatim Autodialer. This should throw

the readings of the instruments off scale. If there is no such effect, your wiring

is not including the Verbatim autodialer in the loop. Verify that the type of

signal source agrees with the physical configuration on the VAN card according

to the marking on the back of the card.

B.1.10 Troubleshooting Analog Grounding Problems for

Verbatim Analog

The most common analog signal type in use in the Verbatim marketplace is

current loops, wherein the signal is a controlled DC current ranging from 4 to

20 milliamperes.

The loop consists of a current transmitter (consisting of a transducer and a

supporting power supply which may or may not be packaged into one unit), and

one or more receiving devices which measure and respond to the current signal

they detect on the loop. The power supply voltage is typically 24 volts DC.

The terms "transducer" and "transmitter" are used interchangeably. The

transmitter's job is to ensure that the current level accurately reflects the

physical parameter which the transducer is measuring (typically a pressure or

liquid level), regardless of what impedance it sees in the loop.

In order to do this, it presents whatever voltage across its terminals is needed to

achieve the correct current flow. This voltage must be great enough to

accommodate the total resistance in the loop. The typical resistance

contribution presented by each receiving device is 250 ohms. However, the DC

resistance presented by the Verbatim analog inputs is around 70 ohms (49.9

ohm precision resistor plus two 10 ohm surge standoff resistors).

In theory, all elements in the loop are isolated from any connection to electrical

ground. This is intended to eliminate concerns about errors in the signal caused

by conflicting ground or other conflicting connections.

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