©Copyright MAC Instruments 2005. All Rights Reserved. MAC155 Rev. 12
Pg 51
The Loop Failure LED located near the +15V input connector indicates an
open loop condition on the 4–20mA loop output.
Alarm LED
The Alarm LED provides visual indication of the Alarm Relay status. If the
LED is illuminated the relay is energized.
Maintenance LED
The Maintenance LED provides visual indication of the Maintenance Relay
status. If the LED is illuminated the relay is de-energized.
Electrical Tests – Probe
The main circuit board in the MAC155 probe has nine (9) LED’s to aid in
diagnosing potential problems with the MAC155 probe.
The probe receives 120V AC power and +/- 15V DC power from the MAC155
controller. Fuses for these lines are located on the back of the controller.
+/– 15V Power
Two LED’s labeled +15V and -15V are located in the upper left of the main
board. Test points are located to the right of these LED’s where the DC voltage
can be measured, (Refer to
Figure 20 – ±15V Power Supply Status Indicators).
The load on the +/- 15V power supplies varies between 100mA and 4A. Thus
the DC voltage measured at the test points may vary and will be less than the
nominal 15V depending on the wire length and wire size between the controller
and the probe, (Refer to “Table 1 – DC Power Conductor Size vs. Length”).
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