Fisher & Paykel MR720 User Manual

12

Ref. 185040646 MR730/720/700/480 Technical Manual ¯ Revision F ¯ Issued March 2001

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.

♦

41 °C calibration probe, available in MR700 series calibration kit (Fisher & Paykel part no. 900MR548).

♦

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 k

Ω

 resistor.

(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 humidifier
front panel.

4

With model MR480 only connect the jumper cable from pin 7 of U10 to the cathode end of D7 on the control
board.

5

With the Chamber Temp button held down turn on the powe r switch. Display should show -1-

6

Using the Chamber Temp button step through to number -4-

7

Adjust VR4 slowly so the display just changes from vertical to horizontal bars (|||||| to ===). Back off VR4 and
recheck that VR4 is not rotated past this display transition point.

8

Using the Chamber Temp button step to number -5-

9

Remove the 41 °C calibration probe.

10

Adjust VR5 for a display reading of zero. ( 0)

(This value may drift over time. A deviation of up to ± 2.0 will not affect circuit performance.)

11

Calibration is complete; do performance check (§ 6.0).

(See § 9.0 for serial number details)