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Otherwise if a heater wire is not connected then the optoisolator will be turned on and off in synchronisation with the secondary cycle. The output of the optoisolator feeds U4 on the control board. This signal, with processor interpretation, provides the information to determine if the Heater Wire is connected or open circuit and also the integrity of fuse F2, the 4 A fuse supplying power to the Heater Wire. Q11 controls power to the heaterplate and is under control of optoisolator U12 and transistor Q12 via an output port (HPC) on U4 on the control board. Resistors R64, R57 limit the gate current to the triac and with C33 form a snubber for the triac and the optoisolator. Transistors Q5 and Q6 are an RS232 level driver for the serial data interface. 4.4 PROBE TEMPERATURE VERSUS THERMISTOR RESISTANCE TEMP (± 0.2 °C) RESISTANCE (W) TEMP (± 0.2 °C) RESISTANCE (W) 0 7352.8 36 1411.3 9 4702.2 37 1355.0 28 1976.6 38 1301.0 29 1893.3 39 1249.2 30 1814.4 40 1199.6 31 1739.2 41 1152.3 32 1667.2 42 1107.3 33 1598.2 43 1064.5 34 1532.9 44 1023.1 35 1470.6 60 560.3 Ref. 185040646 MR730/720/700/480 Technical Manual . Revision F . Issued March 2001 12 5.0 CALIBRATION______________________________________________ 5.1 INTRODUCTION Calibration should be performed after any servicing involving the printed circuit boards. After calibration, perform a performance check as outlined in § 6.0. Note: For instructions on disassembly of the unit, refer to § 7.0. Calibration is facilitated by entering a special Calibration mode. See Appendix A1. There are only two adjustments VR4 (the 41 °C comparator stage) and VR5 ( setting of the span of the A to D converter). This calibration procedure may be carried out if the unit is thought to be out of calibration (E0x to E7x error messages in the display) or if any of the circuit boards have been replaced or repaired. In particular any repair that may have altered the potential of the ± 5 V rails or component change associated with the A to D converter would require a calibration check. Calibration should be checked and performed after the unit has been running for at least twenty minutes; ie after the unit has warmed up. 5.2 EQUIPMENT REQUIRED ¤ 41 °C calibration probe, available in MR700 series calibration kit (Fisher & Paykel part no. 900MR548). For models with Revision D PCB and earlier: ¤ Heater Wire module. ¤ For MR480 only - jumper connector cable, which consists of two easy hooks connected in series with a 100mm length of cable and a 22 kW resistor. 5.3 CALIBRATION PROCEDURE FOR MODELS WITH REVISION D PCBS OR EARLIER (Before Serial Number 92XXAAA05495) (See § 9.0 for change history). 1 With models MR730/720/700 ensure that a Heater Wire module is connected, and that the Heater Wire switch is on (Heater Wire On LED should be on). 2 Plug in the 41 °C calibration probe. 3 Gain access to the adjustment potentiometers VR4 and VR5, by removing the control board from the humidi...

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