GE Hydran 201i, Instruction Manual, Page: 283 / 300

Part 17997 Rev. 6, March 2011 G-1
Appendix G
Unit Conversions
In a current loop, any length of cable and number of devices can be connected in series
provided that the following conditions are met:
• All devices have floating differential inputs ( both leads of signal input are ungrounded).
• The total loop resistance does not exceed 500

.
G.1 CONVERTING CURRENT TO VOLTAGE
Recording devices with voltage inputs can be converted to current inputs by shunting their
input terminals with an appropriate resistor. The resistor value is calculated as follows:
Resistor (

) = 50 x input voltage range (in volts) of recording device
Example: A chart recorder with an input range of 1 V uses a 50-

(1 %, 1 W) resistor
across the recorder input.
G.2 CONVERTING PPM TO MA (OR VICE VERSA)
To convert mA (milliamperes) into ppm (or vice versa), use the following formulas:
ppm = 125 x (mA - 4); or mA = 4 + (ppm

125)
Example: For a 4.8-mA current, the level of gases in oil is 100 ppm. Likewise, if the display
reads 250 ppm, then the current value is 6.0 mA.