420 Oven and Temperature Control
Testing resistance of the heater coil
4 of 20
Jun 2001
Mainframe
Agilent 6890 Gas Chromatograph Service Manual
Testing resistance of the heater coil
If you believe that your heater coil is cracked or otherwise damaged and has
caused an open circuit, you can check it by measuring its resistance.
To measure the resistance
WARNING Before proceeding, turn off the main power switch and unplug the power cord.
Caution Make sure you are properly grounded with an ESD strap before continuing.
1. Turn the instrument power off.
2. Disconnect the oven heater leads (P3, P4) from the AC power board.
3. Use an ohmmeter to measure resistance at the connectors.
Acceptable resistance ranges
Acceptable resistance ranges (in ohms) are given below. Acceptable
resistances range from the nominal value for a new, cold heater to +5% from
the nominal value.
Note Resistance goes up approximately 3% after heating the coil.
Nominal cold heater resistances
Standard oven Fast-ramp oven
120 V 9.07–9.52 Ω n/a
200 V n/a 17.78–18.7 Ω
220 V n/a 21.51–22.6 Ω
230 V 33.06–34.71 Ω 23.51–24.7 Ω
240 V n/a 25.60–26.9 Ω
n/a = not available
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