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ROC364 Instruction Manual

3-10 Input and Output Modules Rev Jun/05

R1=0

LEVEL

DOC0159

O SRC

220

V = OUTPUT VOLTAGE FROM MODULE = 0 TO 5 VDC, 5 mA

COM

VOLTAGE DEVICE

ROC-POWERED

Figure 3-10. Analog Output Source Module Field Wiring for Voltage Devices

3.4.5 Discrete Input Source Module

A schematic representation of the field wiring connections to the input circuit of the Discrete Input

Source module displays in Figure 3-11.

The Discrete Input Source module is designed to operate only with non-powered discrete devices,

such as “dry” relay contacts or isolated solid-state switches. Use of the module with powered

devices may cause improper operation or damage.

The Discrete Input Source module operates by providing a voltage across terminals B and C that is

derived from internal voltage source V

. When a field device, such as a set of relay contacts, is connected

across terminals B and C, the closing of the contacts completes a circuit, which causes a flow of current

between V

and ground at terminal C. This current flow is sensed by the DI module, which signals the

ROC electronics that the relay contacts have closed. When the contacts open, current flow is interrupted

and the DI module signals the ROC electronics that the relay contacts have opened.

A 10-ohms scaling resistor (R1) is supplied by the factory and accommodates a source voltage (V

) of

11 to 30 volts dc. The source voltage is the input voltage to the ROC. However, it is desirable to

optimize the value of R1 to reduce the current drain from the source or reduce the heat generated in

the module due to high source voltage. The formula for determining the value of R1 is given in

Figure 3-11. For optimum efficiency, R1 should be scaled for a loop current (I) of 3 milliamps.

PULSE DEVICE

ROC-POWERED

= SOURCE VOLTAGE FROM MODULE = 11 TO 30 VDC

R1 + R

+ 3.3K = LOOP RESISTANCE = 4.5K OHMS MAX

– R

– 3.3K

= RESISTANCE OF FIELD WIRING

TO OPTIMIZE SCALING RESISTOR R1:

I = LOOP CURRENT = 3 mA TYPICAL

R1 =

– 1

–

N/C

R1=10

3.3K

DI SRC

DOC0143A

Modified

Figure 3-11. Discrete Input Source Module Field Wiring

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