1B21AN データシートの表示（PDF） - Analog Devices

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1B21AN

Isolated, Loop-Powered Voltage-to-Current Converter

Analog Devices 

APPLICATIONS INFORMATION

OUTPUT PROTECTION

In many industrial applications, it may be necessary to protect

the current output from accidental shorts to ac line voltages in

addition to high common-mode voltages and short circuits

to ground. The circuit show in Figure 6 can be used for this

purpose. The maximum permissible load resistance will be

lowered by the fuse resistance (typically 8 Ω) when protection

circuitry is utilized.

FB 18

1B21

VLOOP

1

INPUT 17

REF OUT 19

+15V 20

COM 21

–15V 22

REF

OSCILLATOR

1N4002

38

1N4002

RECTIFIER

50V

0.1µF

FUSE

1/16A (S.B.)

GE

VARISTOR RLOAD

V27ZA1

Figure 6. Output Protection Circuitry

LOW DRIFT INPUT NETWORK

Figure 7 shows a configuration suitable for applications where

errors have to be minimized over a wide temperature range. A

temperature tracking network such as a 50 k Beckman (PN 698-

3R50KD) can be used to implement both offset and gain for

either 0 mA to 20 mA or 4 mA to 20 mA current loops. For

0 V to 10 V signals either IN1 or IN2 can be used for input.

For 0 V to 5 V signals, jumper In1 to In2. Similarly, for 4 mA

to 20 mA operation the 4 mA node should be jumpered to

OFFSET, while for 0 mA to 20 mA it should be tied to COM.

1B21

IN2

IN1

OFFSET

4mA

COM

BECKMAN 50kΩ R/N

FB

18

INPUT

17

1%

24.3kΩ

19

REF

1B21

1

38

+15V 20

COM 21

–15V 22

OSCILLATOR

RECTIFIER

NOTES

1. NODES LABELLED FOR ILLUSTRATION ONLY.

Figure 7. Low Tempco Resistor Network Configuration

MULTILOOP ISOALTION

Multiple 1B21s can be connected to a single loop supply in

parallel as show in Figure 8. The amperage of the loop supply

should be sufficient to drive all the loops at full-scale output.

VLOOP

1

RL1

38

1B21

1

RL2

38

1B21

Figure 8. Multiple 1B21s with Single Loop Supply

Rev. C | Page 7 of 8

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