Jenway 6300 Ser Man
24
5.2
Detector Circuit
Detectors and Amplifiers
The current through the detector D1 (S1133 type fitted) is
proportional to the incident light. IC3a acts as a current to voltage
converter, the gain being set by the feedback resistors in the T
network.
In normal operation pins 3 and 4 of SK2 are linked so the signal
passes to the three amplifiers of IC1. IC1b is set for unity gain,
IC1c has a gain of 10 and IC1d a gain of 100.
A to D Conversion
Each of these amplified signals then pass into the first three
channels (CH0 to CH2) of an 8 channel, 12 bit, serial, A to D
converter.
All three channels are converted and the microprocessor selects the
channel that gives the best resolution without reaching saturation
(32767 counts). In effect this means CH2 will be selected for inputs
up to 40mV, CH1 for inputs up to 400mV and CH0 for inputs up to
4.0V.
The A to d converter requires a reference voltage of 4.096V which
is generated from the 5V rail by D4, this is fed to pin 14, Ref+, of
the A to D converter, IC2.
The E
2
PROM, IC4, maintains calibration data for the PCB, see
Section 8.6 - A to D Calibration.
5.3
Microprocessor and Display
The microprocessor (IC102) is an H8-325 type with 64K linear
address space, its architecture is register based and optimised for
software written in the C language. A 16 bit address bus is used
with an 8 bit external data bus. The 1024 bytes of internal RAM are
shared equally between the internal requirements of the processor
and for the storage of operator set variables. The later are also
stored in non-volatile E
2
PROM to enable the last settings to be
restored after power has been interrupted or switched off.
