7341
Users Guide
8-10
Decomposition: The temperature may reach a point at which decomposition of the fluid
begins. Further increasing the temperature may accelerate decomposition to the point of
danger or impracticality. Silicone oils can oxidize, causing the fluid to thicken. Replace at
the first sign of increasing viscosity.
Stirring
Stirring the bath fluid is very important for stable temperature control. The fluid must be
mixed well for good temperature uniformity and fast controller response. The stirrer is
precisely adjusted for optimum performance.
Power
Power to the bath is provided by an AC mains supply. Refer to Specifications in Chapter
3, for power details. Refer to and read the CAUTION at the front of the manual
concerning brownout and over voltage protection. Check the back panel label for the
correct voltage and frequency prior to energizing the bath. Power to the bath passes
through a filter to prevent switching spikes from being transmitted to other equipment.
To turn on the bath press the control panel power switch to the ON position. The stirring
motor will turn on, the LED display will begin to show the bath temperature, and the
heater will turn on or off until the bath temperature reaches the programmed set-point.
When powered on, the control panel display will briefly show a four digit number. This
number indicates the number of times power has been applied to the bath. Also briefly
displayed is data, which indicates the controller hardware configuration. This data is used
in some circumstances for diagnostic purposes.
Heater
The temperature controller precisely controls the bath heater to maintain a constant bath
temperature. Power is controlled by periodically switching the heater on for a certain
amount of time using a solid-state relay.
The front panel red/green control indicator shows the state of the heater. The control
indicator glows red when the heater is on and green when the heater is off. The indicator
pulses at a constant rate when the bath is maintaining a stable temperature.
Temperature Controller
Fluke’s unique hybrid digital/analog temperature controller controls the bath temperature.
The controller offers the tight control stability of an analog temperature controller as well
as the flexibility and programmability of a digital controller.
The bath temperature is monitored using a platinum resistance sensor as the control probe.
The signal is electronically compared with the programmable reference signal, amplified,
and then passed to a pulse-width modulator circuit that 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 a solid-state relay failure or other circuit failure, the
micro-controller automatically turns off the heater with a second mechanical relay
anytime the bath temperature is more than a certain amount above the set-point
temperature. In addition to this protection, the controller is also equipped with a separate
thermocouple temperature monitoring circuit that shuts off the heater if the temperature
exceeds the cutout set-point.
The controller allows the operator to set the bath temperature with high resolution, set the
cutout temperature, 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 Fahrenheit. The controller is operated
and programmed from the front control panel using the four key switches and digital
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