Thermal Conductivity Analyzer | Model 212R |
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tommustbeevidentwithzerogasflowing. Ifthissymptomisdisplayedonly when the sample is flowing, the problem is related to one (or more) of the five
(5) points outlined in section 7.3.
Tocheckthetemperaturecontrolcircuit,usethefollowingprocedures:
1)With the power switch ON, open the control panel door and check to see if the fan is running. If it is not, check the left hand fuse. This fuse protects the entire temperature control circuit (see schematic). If the fuse will not hold, a short circuit is indicated. Disconnect the printed circuit card and replace the fuse. If the fuse holds (as indicated by the fan running) the printed circuit card will have to be replaced.
NOTE:Unlesscompetentelectronictechniciansareavailable,TAI recommends that a replacement printed circuit card be ordered and the existing board returned to the factory for repair. Repair charges (out of warrantee) will be based on time and material. A schematic of the proportional temperature control card is included among the drawings at the rear of the manual.
2)If the fuse will not hold with the board removed, a short is indi cated in the fan, the heater resistors, or the interconnecting
wiring. With the board removed, check wiring and components for short circuits.
3)If the fan is running, connect an AC volt meter across anyone of the heater resistors on the fan assembly (the meter should be set to read 50 VAC). In a properly operating circuit, the meter should read approximately 47 volts (heater control full on) as the control panel is open and the thermistor should be demanding maximum heater voltage. If no voltage is present, either the circuit card or the thermistor probe is faulty. Isolate the problem by first disconnecting the circuit board from its socket and with
an ohmmeter check between terminals 5 and 6 of terminal strip TS2. If a reading is obtained (disregard actual resistance) the thermistor is intact and a new circuit card will be necessary. If no reading is obtained, a new probe assembly will be required.
4)If approximately 47 VAC is measured across the heater resis- tors, a runaway, or correct, circuit is indicated. To determine which is the case, hold a soldering iron in close proximity (1/2") to the end of the thermistor probe and observe the meter.
Teledyne Analytical Instruments | 23 |
