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7
General operation
The components, features and operational theory of the Model 6055 calibration
bath are described in this section.
The Model 6055 calibration bath is shown in block diagram form in Figure 4
on page 24. This diagram illustrates the primary features of the bath system and
their function, which are described as follows.
7.1
Two modes of temperature control
There are two modes of temperature control available with the Model 6055.
The Temperature Control mode or the Temperature Drift mode may be selected
by a switch on the front panel.
7.1.1
Temperature control mode
The Temperature Control Mode uses a hybrid digital/analog PI temperature
controller with a lock-in-amplifier. The bath stability is very high with this con-
troller. The temperature is selected using the four button keypad on the front
panel. Temperatures from 150 to 550°C may be selected directly to a hundredth
of a degree. Finer adjustment is available using the vernier adjustment. Accu-
racy of the setting is typically ±0.5°C or better.
The controller pulses AC current to the control heaters in a time modulated
fashion to compensate for heat gains and losses to the system. A two color LED
on the control panel glows red when the heaters are on and glows green when
they are off and cooling is taking place. (Note: The cooling required for control
is supplied through heat loss to ambient).
The temperature control probe uses a 100 ohm PRT. Plug the probe into the
rear of the control unit.
The heaters are internal to the tank. They are arranged electrically to provide
the 4 control heating positions plus an off position. The additional boost heat-
ing position is accessed from a separate switch on the control panel.
7.1.2
Temperature drift mode
When using the Temperature Drift mode, the heater may be set manually to al-
low the temperature to drift very slowly (a few millidegrees C per minute) over
the desired range. This allows the control noise to be eliminated although
greater skill is required in making calibrations. The heater power is adjusted by
means of a variable transformer located on the control panel. It allows position
one of the heater selection switch to be continually variable from 0 to 100%.
Positions 2, 3, 4 and Boost add their full value of heat incrementally to the ad-
justed value of position 1.
7 General operation
Two modes of temperature control
23
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