Teledyne 402REU - Hydrocarbon analyzer - Manual (Page 42)

Chapter 5 Model 402 R-EU
Teledyne Analytical Instruments 5-8
NOTE: If any of the components located inside the isothermal chamber has
failed, the instrument must be removed for service. The sample
selector module can be unplugged for service. All other compo-
nents can be reached without instrument removal.
5. If no problems are found with either the thermistor or the heater
circuits, then replace the temperature control board.
5.3 Ignition and/or Flame Guard Circuit Checks
If the flame guard circuit will not hold the flame-out lamp off when
the ignition procedure is employed (see Chapter 3: Flame Ignition), per-
form the following procedure to isolate the problem (consult the system
schematic for details of the circuit):
1. Disconnect connector J3 (4 sockets) from connector P3 (4
pins). These are one of the large pairs of connectors just outside of
and to the left of the isothermal chamber. See Figure 5-2.
2. Check the flame guard sensing thermistor by measuring the resis-
tance between pins 1 and 2 of P3. The nominal resistance at
25°C is 100K, resistance readings at about 25°C of greater than
250K or less than 40K indicate that the thermistor is defective and
should be replaced.
3. Check the anode-igniter coil for continuity by measuring
between pins 3 and 4 of the disconnected cable plug P3. The
ohmmeter should indicate a maximum resistance of 1
Ω
.
4. If either step 2 or 3 does not check as indicated, remove the
electrode assembly of the detection cell and return it to the
factory for repair. If the quartz flame tip is damaged, the top
section of the cell may be removed by disconnecting the vent
line, and removing the screws around its flange. Return the unit
complete with attached electrode cable. If steps 2 and 3 both
check out properly, reconnect the anode-igniter cable (connect
J3 to P3).