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...4 LIQUID HANDLING SECTION
'Out of Sample' condition. This switch is used by the monitor to
initiate the 'Out of Sample' alarm.
b) From the bottom of the constant head unit the sample is
drawn through the normally open ports of the solenoid valves
SV1 and SV2 by one channel of the peristaltic pump.
c) The reagent is drawn through another channel of the
peristaltic pump, and is then mixed with the sample. The tube
diameters are arranged so as to obtain the correct ratio of
sample and reagent.
d) The electrodes are housed in a temperature controlled
flowcell which includes a heat exchanger to remove the
effects of sample and ambient temperature variations. The
electrodes produce an electrical potential when exposed to
the reacted sample, which is proportional to the concentration
of the ion being measured. The electrodes are connected to
the electronic section where, after digital conversion, the
signal is processed by the microprocessor.
e) After measurement the sample flows to waste via the
contaminated drain connection.
f) During calibration the monitor introduces two calibration
solutions sequentially in place of the sample by means of the
solenoid valves SV1 and SV2.
Microprocessor Unit
External
Serial
Interface
Connections
Heater
Control
8
User Junction
Box
Interconnection
Cables
Out of Sample
Float Switch
Probe
Sample/Calibrate
Soleniod Valves
Liquid Handling
Section
Fig. 5.1 Electrical Connections Layout
5 ELECTRONICS SECTION
5.1 Electronic Layout – Fig. 5.1
The electronic section comprises two separate sections:
•
The User Junction Box at the top right hand side.
•
The Microprocessor Unit at the top left hand side.
5.2 User Junction Box
This unit contains the relays for the heater, solenoid valves and
alarms, and all the user external connection terminals, with the
exception of the serial interface (if fitted).
Once installed there should be no need to remove the junction box
cover on a regular basis. However, to assist in any fault finding
procedure, there are light emitting diodes (l.e.ds) on the printed circuit
board (p.c.b.) to indicate if the relays and heater are being energised.
Switches for the mains and pump/heater are situated on the right
hand side of the junction box, together with a mains indication
lamp and mains fuse – see Fig. 2.3.
5.3 Microprocessor Unit
This contains the analogue input processing, microprocessor,
alarm and current output generation, and (if fitted) the serial
interface output.
The programme controls, digital and dot-matrix displays, alarm
indication and status l.e.ds are all mounted on the front panel of
the microprocessor unit.
Mains Supply 115 / 230 V
Concentration Alarm Relays
Calibration Mode Relay
Out of Service Relay
Out of Sample Relay
Current Outputs
Pump
Heater Block
External
User
Connections
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