Heater fuses are located internally. See Section 13, Troubleshooting, for more
information
8.5
Cooling
WARNING:
Do not use cooling water at temperatures approaching
100°C. When operating the bath at these high temperatures make sure the
hoses are disconnected and completely drained, otherwise there may be
danger of steam explosion.
Cooling water or other external coolant circulates beneath the bottom of the
bath tank to provide cooling. The cooling fluid must be of constant temperature
and flow rate for good temperature stability. For optimum control stability the
temperature difference between the cooling water and bath fluid should be
about 20°C. Temperatures for this fluid below 15°C are not recommended.
Attach
1
4
inch I.D. hose lines to the tubes protruding from the back of the bath.
Fasten the hoses tightly with hose clamps. Cooling fluid pressure should not
exceed the capability of the lines attached. Connect a valve in line with the
cooling water to regulate the flow rate. Run the outlet line to a drain or tank.
The cooling fluid must match the properties required for the bath temperature.
Fluids should have the same safety margin and careful consideration as any
fluid used in the bath.
8.6
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 platinum resistance sensor in the con-
trol probe. The signal is electronically compared with the programmable refer-
ence signal, amplified, and then fed to a pulse-width modulator circuit which
controls the amount of power applied to the bath heater.
The bath is operable within the temperature range given in the specifications.
For protection against solid-state relay failure or other circuit failure, the mi-
cro-controller will automatically turn off the heater with a second mechanical
relay anytime the bath temperature is more than a certain amount above the
set-point temperature. As a second protection device, the controller is also
equipped with a separate thermocouple temperature monitoring circuit which
will shut off the heater if the temperature exceeds the cutout set-point.
The controller allows the operator to set the bath temperature with high resolu-
tion, set the cutout, adjust the proportional band, monitor the heater output
power, and program the controller configuration and calibration parameters.
The controller may be operated in temperature units of degrees Celsius or Fahr-
6020 Series Calibration Bath
User’s Guide
36
