Ocean Optics NeoFox - Manual (Page 72)

C : Analog Output
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Resistor / Volt Meter
If an ammeter is not available, as is the case with many data acquisition systems, a voltmeter can be used
instead (see following figure). To use a voltage measurement system, users should select a low-
impedance resistor and a high-impedance voltage measurement instrument.
Be aware that there will be a voltage drop across the resistor that “substracts” from the loop voltage
supply. The voltage drop can be calculated as resistance times current. For example, a 100 Ohm resistor at
20 mA would have a 2 volt drop across it. If the power supply was 12 V, then the loop voltage would
actually measure under 10V and the system would be outside of specification (11V is the minimum
specified loop voltage). It is important to select a resistor that will not “subtract” too much from the loop
voltage.