Ocean Optics NeoFox, Installation And Operation Manual

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C: Analog Output
54 013-20000-009-02-201510
Users should be aware of any possible connections between NeoFox and their interface circuits
when setting up their hardware.
4-20 mA Isolation
Some users (especially those in industrial settings) may need to use an isolated 4-20 mA loop.
Unfortunately, the current sink on the NeoFox unit is not isolated and is not suitable for use in
environments which may cause the loop voltage to exceed 30V. However, there are a number of third-
party products available that can convert the output of the NeoFox into an isolated 4-20 mA loop
transmitter.
Some suitable products include:

LPI-1

Manufacturer: A Pi ( http://www.api-usa.com )

Suggested Vendor: Mod-tronic. (
http://www.mod-tronic.com
)

Part Number: LPI-1

931S-A1A1N-IP1

Manufacturer: Rockwell Automation

Suggested Vendor: Varies by geographic region

Part Number: 931S-A1A1N-IP1

931S-C1A2D-OP*

Manufacturer: Rockwell Automation

Suggested Vendor: Varies by geographic region

Part Number: 931S-C1A2D-OP
*This part can be used to convert the 0-5V output of the NeoFox into a 4-20mA signal.
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.