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MR810 Technical Manual Revision C REF 185042601
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3.5 OPERATION
The MR810 humidifier has two modes of operation: (a) heater-wire mode and (b) non heater-wire mode.
3.5.1 HEATER-WIRE MODE
Connecting a heated wire breathing circuit (between 10 and 28 Ω) to the MR810 will automatically initiate
the heater-wire mode of control. The flow detection algorithm starts, and the Heater-wire Indicator in the
heater-wire connector illuminates.
Flow Detection State
At power-on the MR810 controls the heater plate to a fixed temperature dependent on the setting (40 °C at
Low, 50 °C at Medium and High). The humidifier monitors the power required by the heater plate to
maintain this temperature. Once the system is stable (about half an hour), the humidifier estimates the gas
flow rate based on the power required. The humidifier then initiates the normal control state. With the
temperature measured by the chamber sensor thermistor, the humidifier can identify the type of ch amber
(reusable or single use) being used and control accordingly.
The humidifier applies power to the heater-wire circuit dependant on the ambient temperature and the mode
selected.
Normal Control State
Once the flow has been estimated, the humidifier controls the heater plate to a fixed temperature based on
the estimated flow. The humidifier then continues to monitor the heater plate temperature and power
consumption for changes. Any significant power change (due to a change in flow, chamber run out of water
etc.), will cause the humidifier to switch back to the flow detection state. Small power changes will caus e
the humidifier to step the heater plate temperature up or down to compensate for the change.
Mains Voltage Compensation
The humidifier automatically compensates for fluctuations in mains voltage to accurately control the power
being delivered to the heater-wire and heater plate. Compensation is limited to ± 10 % of rated operati n g
voltage.
Ambient Temperature Compensation
In the heater-wire mode of operation, cold ambient temperatures will cause the humidifier to automatically
increase the heater-wire power, minimising the condensate in the breathing circuit. Conversely for high
ambient temperatures the heater-wire power is automatically reduced.
Ambient temperature compensation is limited to between 18 and 30 °C, as shown in Figure 3. 4, effect i vely
limiting the maximum effect due to ambient temperature compensation.
Ambient Temperature vs. Heater Wire Power
0
5
10
15
20
10 20 30 40
Ambient Temperature (°C)
Heater wire power
(Watts)
Low
Medium
High
Figure 3.4: Heater-wire power over the ambient temperature 10 to 40 °C
Mode Level