Appendix K. Unit Conversions
K-1. Analog Outputs – Converting ppm to mA (or Vice Versa)
To convert mA (milliamperes) into ppm (or vice versa), use the following formulas:
• 0–1 mA configuration: ppm = 2,000 x mA; or mA = ppm 2,000
Example: For a 0.025-mA current, the level of gases in oil is 50 ppm. Likewise, if
the display reads 150 ppm, then the current value is 0.075 mA.
• 4–20 mA configuration: 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.
K-2. Moisture Level and Relative Humidity (Converting to ppm
Concentration)
The relative saturation (RS), often called the relative humidity (%RH), is expressed
in units of percent. It is the concentration of the water dissolved in the oil (PPM),
relative to the solubility or concentration of water the oil can hold (PPMs) at the
measurement temperature, as shown in Equation 1:
where PPM and PPMs are in weight/weight
In Equation 1, RS is measured by the Hydran M2-X. We need to know the PPMs in
order to calculate the PPM.
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