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7012 Calibration Bath
User's Guide
8.5
8.6
8.7
34
The front panel red/green control indicator shows the state of the heater. The
control indicator glows red when the heater is on and glows green when the
heater is off. The indicator will pulse constantly when the bath is maintaining a
stable temperature.
The heater has two power level settings. The "HIGH" heater power setting is
used to quickly heat up the bath fluid to the desired operating temperature. The
"HIGH" heater power setting may also be required for control at high tempera-
tures. The "LOW" setting is used for control at lower temperatures and for
scanning at slower rates. When controlling at the "HIGH" heater power setting
instead of "LOW" the proportional band may need to be increased (typically by
a factor of four) to compensate for the increase in power gain. Otherwise the
temperature may oscillate.
Cooling
The back pressure control valve limits the cooling capacity of the unit. It will
normally be open all the way (full CCW) for temperature slewing and opera-
tion. If during operation the front panel meter indicates excessive cooling, this
valve is closed partially (turn CW) until the percentage of heating to cooling is
brought into line. It is necessary to wait a few minutes after each adjustment
until the system settles.
Set the COOLING TEMPERATURE according to the cooling label. The cool-
ing temperature should NOT be set above 90 psig. At about 45°C the refrigera-
tion will not be required as there is sufficient cooling to the room. Wait a few
minutes after each adjustment until the system establishes itself. Readjust if re-
quired after settling for a while.
For maximum cooling for slewing to lower temperatures, the BACK PRES-
SURE valve should be fully open and the COOLING TEMPERATURE set to
0°C. Readjust higher or lower as required after set temperature is reached.
Fluid Drain
The drain at the back of the bath (see Figure 4 and Figure 5 on pages 24 and
25) may be used to remove fluid from the bath. During operation of the bath
the drain must be closed.
Temperature Controller
The bath temperature is controlled by Hart Scientific's unique hybrid digi-
tal/analog temperature controller. The controller offers the tight control stability
of an analog temperature controller as well as the flexibility and programmabil-
ity of a digital controller.
The bath temperature is monitored with a linear thermistor sensor in the control
probe. The signal is electronically compared with the programmable reference
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