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7103 Micro-Bath User's Guide
Power
8.5
Power
Power to the bath is provided by an AC mains supply and passes through a fil ter to
prevent switching spikes from being transmitted to other equipment. Re fer to Section
3.1, Specifications, for power details.
To turn on the bath, switch the control panel power switch to the ON position. The stir
motor will turn on, the LED display will begin to show the bath tem perature, 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 and version
number. This data is used in some circumstances for diagnostic purposes.
8.6
Thermal Electric Devices (TED)
The power to the bath is precisely controlled by the temperature controller to maintain
a constant bath temperature. Power is controlled by periodically switching the TEDs
on for a certain amount of time using power transistors.
8.7
Fluid Drain
The fluid may be drained from the 7103 by tightly screwing the transport/pour access
lid onto the top of the bath and pouring the liquid into an appropriate container.
8.8
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, a bi-me tallic cut-out
automatically turns off the heater anytime the bath temperature exceeds the maximum
temperature.
The controller allows the operator to set the bath temperature with high resolu tion,
adjust the proportional band, monitor the heater output power, and pro gram 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 LED
display. The controller is equipped with a serial RS-232 digital interface for remote
operation. Operation using the digital interfaces is discussed in Section 10, Digital
Communication Interface.
28
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