Models 3940 and 3949_________________________________________________________________Control Panel Operation
3 - 1
3.5 Overtemp Safety Control, Indicator Light, and
Audible Alarm
The overtemp safety thermostat should be set slightly
above the operating temperature of the incubator. In the event
of an overtemp condition, the overtemp safety thermostat will:
• Activate the audible alarm and the overtemp indicator
light.
• Interrupt power to the heaters and maintain the incubator’s
cabinet temperature at the overtemp safety control point.
Note: The overtemp control is not directly calibrated. The
numbers (0 to 10) on the dial are for reference only and do not
correspond to any specific temperature.
If an overtemp condition occurs, the alarm can only be
silenced by raising the overtemp safety thermostat setting.
However, the cause of the problem must be determined and cor-
rected before normal operation under the main temperature con-
troller is resumed.
3.6 Humidity Controller
The humidity controller knob is used to set the level of
humidity desired in the chamber.
3.7 Humidity Range Selector Switch
The humidity range selector switch is used to select the
proper humidity range for the desired level of humidity in the
chamber.
~Low Range: 10% to 50% rH (Lower Scale)
~High Range: 40% to 96% rH (Upper Scale)
The range selector switch must be set before the desired
percent of humidity is established on the humidity controller.
3.8 Humidify Switch and Indicator
The humidify switch controls the power to the humidity
boiler circuit. The boiler heaters will operate only if there is suf-
ficient water in the boiler. The humidity indicator light is acti-
vated when the humidity switch is in the On position.
3.9 Relative Humidity Indicator
The relative humidity indicator provides a direct readout of
chamber humidity in both ranges.
Section 3 - Control Panel Operation
3.1 Main Power Switch & Indicator Light
The main power switch controls power to the incubator.
The main power indicator lights when the power switch is on
and the unit is receiving power.
3.2 Refrigeration Switch & Indicator Light
This switch controls power to the refrigeration system. The
refrigeration switch should be in the On position when the incu-
bator setpoint temperature is 4°C above ambient or below. The
refrigeration indicator lights when the refrigeration switch is On
and the compressor is receiving power.
3.3 Defrost Switch & Indicator Light
The defrost switch controls power to the defrost system.
The defrost timer is factory set to provide two 15-minute
defrost cycles during a twenty-four hour period. The defrost
switch should be in the On position when the temperature set-
point is 10°C or below.
CAUTION! Failure to turn the defrost switch On when
required will cause icing of the refrigeration coil, which in
turn will impair performance.
The defrost timer is energized by the main power switch,
but timed defrosting can occur only when the defrost timer is in
the On position.
The defrost indicator lights when the defrost switch is On
and the incubator is in a defrost cycle. The indicator light will
go out when the defrost cycle is completed.
3.4 Digital Temperature Controller
The solid state digital thumbwheel switch controls power
to the incubator heater circuit. On a demand for heat, the tem-
perature controller energizes the heaters to bring the tempera-
ture up to setpoint.
On the controller face are three manually adjustable rotary
discs, for direct dialing of the chamber setpoint temperature.
Temperature settings are made by gently rotaing the indiviual
discs until the digits corresponding to the desired setpoint tem-
perature show in the controller windows. The disc on the
extreme right is used for setting temperature in 0.1°C. Settings
0 to 0.9°C can be selected using this disc. The two discs to the
left are adjustable from 0 to 60°C.
The indicator light, adjacent to the temperature controller,
cycles with the chamber heaters to indicate when there is a
demand for heat to meet setpoint requirements.
