Earth grounding, Earth grounding 167 – Watlow Series D8 User Manual
Page 185
Series D8 User’s Guide
Chapter 7: Troubleshooting and Reconfiguring
Doc. 0600-3120-2000
Watlow Anafaze
167
•
For thermocouples, remove the thermocouple leads
and use a digital voltmeter to measure the resistance
between the positive and negative thermocouple
leads. A value of 2 to 20
Ω
is normal. Readings in
excess of 200
Ω
indicate a problem with the sensor.
•
For RTDs, measure between the IN+ and IN- termi-
nals of TB1. RTD inputs should read between 20
and 250
Ω
.
5. To verify that the controller hardware is working correct-
ly, check any input (except an RTD) as follows:
a) Disconnect the sensor wiring.
b) In the Input menu, set the Input type parameter to
J thermocouple
.
c) Place a short across the input. On the loop that you
are testing, the controller should indicate the ambi-
ent temperature.
Earth Grounding
If you suspect a problem with the ac ground or a ground loop:
•
Measure for ac voltage between ac neutral and panel
chassis ground. If ac voltage is above 2 Vac, then there
may be a problem with the ac power wiring. This should
be corrected per local electrical codes.
•
With ac power on, measure for ac voltage that may be
present between control panels’ chassis grounds. Any ac
voltage above 2 Vac may indicate problems with the ac
ground circuit.
•
With the heater power on, check for ac voltage on ther-
mocouples. A control output providing power to the
heaters will increase the ac voltage if there is heater leak-
age and an improper grounding circuit. Measure from ei-
ther positive or negative thermocouple lead to ac ground.
AC voltage above 2 Vac may indicate the ground lead is
not connected to the D8 TB2 ground terminal.
If the above tests indicate proper ac grounding but the control-
ler is indicating incorrect temperatures or process readings:
•
Verify which type of sensor is installed and that the Input
type
parameter in the Input menu is set accordingly.
•
For an RTD or process input, check that the correct input
scaling resistors are installed (see Installing Scaling Re-
sistors on page 172) and check the input scaling parame-
ter settings (see Setting Up a Process Input on page 88).
•
If readings are erratic, look for sources of electrical