Teledyne 100AH - page 148

Teledyne API Model 100AH SO2 Analyzer Instruction Manual, 02417, Rev. D
10.3.3.4 4-20 mA Current Output
4-20 mA current loop option replaces the voltage output of the instrument with 4-20 mA current
output. The current outputs come out on the same terminals that were used for voltage outputs
(see Figure 2-2). It is programmable for 4-20mA or 0-20mA and has a 1500 V common mode
voltage isolation and 240 V RMS normal mode voltage protection. Vloop = 28 V max which is
sufficient to drive up to a 1000 ohm load. Verify that the jumpers on the motherboard are set
properly for the current output mode (refer to schematic 01087 and 01248). See
Section 10.3.2.1 for the 4 - 20 mA current output calibration procedure.
There are two methods to measure the output of 4-20mA option.
1. Voltage method - preferred method
Digital type Multi-meters (DMM) are ideally suited for this type of measurement because of
their high input impedance - usually 10 M ohm or greater. The total load resistance should be
between a 200ohm (min) to 1000 (max), precision load resistor of 0.1% tolerance or better is
recommended.
2. Current method
Although current is constant in a series circuit, accuracy in this type of measurement is
usually less precise than with the voltage method due to the type of circuitry used in digital
multi-meters. Connect a load resistance (between 200 - 1000 ohm) in series with the DMM.
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