Measuring The Current Loop Output - Vega FiberFlex LFXG-H Operating Instructions Manual

Calibration
To correlate the 4 ... 20 mA to the process value, set the span of the current
loop output.
Note: The current loop and process spans are independent and set
A direct measurement of the current is preferable: hook the meter up in
series with the instrument and the DCS. However, if you know the
resistance of the DCS, use a voltage measurement to calculate the current.

Measuring the current loop output

Detector
Terminal block pins
housing
Before a current loop calibration:

Connect an ammeter or the DCS to:
• Terminal connections 13 (mA +) and 14 (mA -)
• Test points H1 and H2
• Anywhere along the current loop
 Make sure there is a 250 – 800  load on the current loop. If no load or
an insufficient load exists on the loop, it may require temporary
placement of a resistor across terminals 13 and 14. Hook the meter or
DCS in series with the load resistor.
42
separately. The current loop span sets the level indications for
the 4 mA and the 20 mA outputs. The process span sets the
endpoints of the calibration curve.
R
t
Current meter
13 and 14
DCS
Detector
housing
LFXG-H Installation and Operation Guide
R
t
Voltmeter
Terminal block pins
13 and 14