4.40 PCB RR-120 MOTHERBOARD REF
5010-120
Temperature control
General Description
The temperature control takes care of the correct temperature inside the flow-through cuvette or inside the
standard cuvette adaptor. The temperature is selectable by the program at fixed levels, i.e. 25 °C, 30 °C or
37 °C.
The temperature control circuit consists of:
•
microcontroller
system
•
temperature
sensor
•
analogue-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 controlling 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 unit IC3 (87C52PLCC) converts the frequency to a digital value.
The voltage signal of the temperature sensor LM335 is typical 3.1 V
DC
at 37 °C,
3.03 V
DC
at 30 °C and 2.98 V
DC
at 25 °C.
The ADC converts the input voltage to a digital value between 0 and 32767 as shown on following diagram:
ADC
input voltage
of temperature sensor
32767
0
ca. 17000
ca. 13900
3,03 VDC
2,98 VDC
3,1 VDC
ca. 15200
RIELE BERLIN
Photometer 5010 V5+
4.40.9
17.03.2009
