A radical approach is required.
We propose abandoning the system in its entirety from the point where PLCs send the data to the SCADA, and build a new system from the UV modules up to that point.
(See attached drawings.)
We have a conceptual scheme although it needs a lot more work before we could start to design the cards we need.
It will, of necessity, be a major scheme.
There are 56 modules containing a total of 2240 lamps in four channels to monitor.
This means we will require 56 new design 'DCA' cards 280 new design 'LCA' cards as well as two new modules for the existing PLC (Telemechanique), which may be retained, but will need new software.
We would prefer to use Modicom PLCs as these are the Company's standard.
Its output will still link into the SCADA system via the LAN.
We will also have to replace the wiring and connectors from the modules to the control cabinets, as there are insufficient ways in the current cables for our system to operate.
The new 'DCA' cards will eliminate the need for a lot of external equipment. The 'black boxes' (RS422/RS232 multiplexers), MODBUS conversion and associated wiring will not be required for the proposed system. This will permit a very simple I/O and 4-20mA signals to be used.
Our proposed system will monitor the following parameters:-
Module temperature, (necessary because of the wet cooling system)
UV lamp status, simple on or off.
UV intensity.
Integrity tests for power supply, distribution etc.
To access to the UV plant data for maintenance, the local operator interface (LOI) would be replaced with a touch screen panel PC with access to the SCADA data via the works LAN.
The only data not directly available will be:- Lamp hours and lamp cycles, but these could be added to the SCADA program if required.
The only function not proposed is control of the relay for flow pacing.
This design has some drawbacks, these are:-
- We cannot do the installation piecemeal so there will be downtime when reporting will not be available.
- It will require new software for the PLCs (although similar software is in use at St Agnes, and may possibly be adapted)
- We will have to install new cables and connectors between the modules and the control cabinets. (The cabinets will need to be sealed and air-conditioned, 4 number)
- Cost. It will be a major project and will take many weeks to complete.
The advantages are:-
- It is simple, understandable, and will work.
- It will provide the essential data required.
- It eliminates the unreliable elements in the current system.
- It is much simpler electronically, giving more reliability and less maintenance.
- Better noise immunity - the simple bus system has no critical timing requirements or practical cable length limitations.
- The data will be more secure.
- Missing "Offline modules" will not cause a problem.
- Spare parts will be readily available within the UK at reasonable cost.
Recommendation
We have had only a very short period to investigate this project.
Whilst we are confident that we have correctly identified the only way forward, we do need to do more research to ensure there are no further services "buried "in the existing system which we have missed.
We also need to ensure that our changes will not prejudice any of the SCADA's other functions.
We also need to speak to the people who will programme the PLCs for us, we must be certain that it can address the proposed data bus system, this is very different from the current serial communications and needs to be understood by the programmer.
Assuming this work is successful we can then prepare the necessary designs, this in turn will enable us to cost the project more accurately.
SYSTEM DIAGRAMS
COS-16
'Black
Box'
Existing UV Monitor System
Proposed UV Monitor System 
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