Table of Contents
Advertisement
7100 Calibration Bath
User's Guide
8.3
8.4
8.5
34
Power
Power to the bath is provided by an AC mains supply of 230 VAC (±10%), 60
Hz, 20 A (50 Hz optional). Power to the bath passes through a filter to prevent
switching spikes from being transmitted to other equipment.
To turn on the bath switch 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 num-
ber. 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 power to the bath heater is precisely controlled by the temperature control-
ler 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 glows green when the
heater is off. The indicator pulses constantly when the bath is maintaining a sta-
ble temperature.
The heater has two power level settings. The "HIGH" heater power setting is
used to quickly heat the bath fluid up 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.
The heaters are protected against excess current due to short or failure by two
10 amp fuses. The fuses are accessed at the back panel of the bath.
Cooling
The Model 7100 refrigeration system is a 2-stage cascade system. This means
there are two individual refrigeration systems or stages. The first stage cools
down or provides cooling for the second stage. The second stage cools the bath.
This type of system is required to attain very low temperatures. The refrigera-
tion system runs continuously when cooling is required.
The first stage is an air-cooled unit using the refrigerant R-507. The fins of the
air-cooled condenser must be kept clean. Dirty condensers cause inefficiency
Advertisement
Table of Contents
