Models 375 (Including Series One), 375/1, 375/2 & 375/4 Section 5
Ludlum Measurements, Inc. Page 5-8 May 2017
4 to 20 mA Isolated Output Driver Option
4 to 20 mA Driver (Isolated) Modification Kit Part Number 4558-104
This circuit may be added to replace the Model 375 analog output, providing
an isolated 4 to 20 mA output capability. The circuit board (LMI Part
Number 5396-754) takes the analog output, varying between 0 and 5.00
volts, and converts it to a current output of 4 to 20 mA.
The circuit has an internal loop supply, generating +12 Vdc from the
RAWDC of the Model 375. It is designed for a 2-wire configuration, with
one conductor carrying the 4-20 mA current signal and the second
conductor providing a return (isolated loop ground). See Wiring Diagram,
Figure 4 (below).
Figure 4: Wiring Diagram.
Decade “Base” Display mA Value
0 0.1 4 mA
1 1 7.2 mA
2 10 10.4 mA
3 100 13.6 mA
4 1000 16.8 mA
5 10,000 20 mA
mA value = 4
.
3.2log
Display reading = 10
.∗
.
∗
5396-754
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