TROUBLESHOOTING AND DIAGNOSTICS
REFERENCE OR OVERRANGE ERROR
6 - 6
REFERENCE OR OVERRANGE ERROR
If an error code is displayed on the Type CTT terminal that indicates a
reference or overrange error, the analog input may be overranged. To
isolate the problem:
1. Measure the common mode voltage on each input (+/–) to earth
ground (Fig.
2. In an ideal single point grounding system, there will be no poten-
tial difference between DC system common and earth ground.
3. The voltage between the analog input (+) and earth ground can
be between -5 V and +10 VDC or AC peak maximum.
4. The voltage between the analog input (–) and earth ground can
be between -10 V and +5 VDC or AC peak maximum.
5. If the analog input exceeds these limits, the controller is properly
sensing an overranged input. The installation must be corrected.
6. Check for single point grounding, the need for input isolators, sig-
nal wiring which is improperly routed with power wiring, inadequate
shielding, etc.
7. Function code 230, S12 = 0, will trip the controller on a reference
voltage error. The alarm summary screen will indicate bypass error
mode.
8. Refer to the status information under
in Section 5 and
reference status byte information.
Figure 6-2. Checking Common Mode Voltage
250
Ω
AI +
AI –
TB2-1
TB3-4(
)
EARTH GROUND/
AC SAFETY GROUND
DC SYSTEM
COMMON
TP80435B
TB1-3
TB1-2