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OnGuard® Smart 4-20 mA Calibration
Introduction
The OnGuard is capable of 4-20 circuit calibration through the
internal web interface
. The 4-20 circuits are set by
firmware default values such that the current loop levels will be very close to 4 and 20 milliamps on average. However,
due to slight performance differences in electronic components, the firmware default levels may not be close enough for a
particular application. Each of the four circuits may be individually calibrated by the end-user. It should be noted that even
though the calibration adjustments can set the levels to within 0.005 mA, the circuits may drift slightly after calibration due
temperature change or other external forces.
Preparation
1. Connect the OnGuard to
external power (12-36 vDC, pin 11 negative pin 12 positive)
. The
OnGuard
’s 4-20
circuits will not operate under battery and will operate only when external power is applied.
2. Connect a suitable ammeter to a selected channel on the OnGuard. Refer to the images below for output
information. At this point, the current displayed on the ammeter will represent the selected channel’s output
(e.g. humidity on channel 4).
Signal
Positive
GND/Common
Chan 1 (Copper)
2
1
Chan 2 (Silver)
4
3
Chan 3 (Temperature)
6
5
Chan 4 (Humidity)
8
7
Chan 5 (Pressure)
10
9
Table 1: Connector Pin Assignments
3. Connect the OnGuard to the PC/MAC with an Ethernet cable and access the web interface.
4. The current output is located on the web interface in the “Settings” tab. At this point, the current displayed on the
ammeter will represent the output channel (1-4) and level (min or max) as selected on the 4-20 calibration
window.
The OnGuard will hold the selected level, bypassing normal 4-20 functionality, for a period of 60 seconds every
time an adjustment selection from this window is chosen.
