Riele Photometer 5010 - Temperature Control

4.40 MOTHER BOARD RR-115 ID 5010-115
RIELE BERLIN Photometer 5010 / V4 4.40.9 22.09.2003
Temperature control
General Description
The temperature control takes care for the correct temperature inside the flow-through cuvette or inside the
disposable cuvette adaptor, i.e. 25, 30 or 37 degrees Centigrade, selectable by the program.
The temperature control circuit consists of:
• microcontroller system
• temperature sensor
• analog-digital-converter (ADC)
• heating unit
• cooling unit
Microcontroller System
The temperature control circuit is a PID-controller, a software module in the microcontroller system. The PID-
controller works in the background all the time. Dependent on the cuvette adaptor the PID-controller uses
different parameters.
The required value of temperature is ascertained by the program of the microprocessor system. The
temperature is controlled according to the set temperature in the selected method.
The PID-controller gives information to the higher program about the given temperature tolerances and
therefore about the readiness for measuring.
Temperature Sensor and ADC
The voltage signal of the temperature sensor LM335 is converted by the IC2 (LTC1286) to an equivalent
frequency. The microcontroller system IC3 (8031PLCC) converts the frequency to a digital value.
Heating
The control variable of the controller has influence on the heating. A switched Darlington transistor in source of
power-switching is used as heating element. The PID-controller produces a voltage at the emitter of the
Darlington transistor by a pulse-width-modulation. This voltage controls the current through the transistor.
Involved components are the microcontroller system IC3 (8031PLCC), the OP-booster IC1A (LM324) and the
MOS-Fet T3 (BS170).
Cooling
For cooling or counter cooling during heating the microcontroller system switches on a Peltier element. There
are four possible levels with following terms and meaning:
0 = Cooling out
1 = Cooling (low level)
2 = Cooling (middle level)
3 = Cooling (high level)
In case of temperature changing by method selection cooling level 0 is selected if desired temperature is
higher as selected one.
In case of temperature changing by method selection cooling level 3 is selected if desired temperature is lower
as selected one.