In This Issue
- The Relationship between Profit, Best Practice and Risk in Automation Projects
- Managing Risk for Integration with Legacy Field Equipment
- Three Fundamental Approaches to Managing the Risk
- Key Risk Items When Upgrading Control SystemsSpecific Advice for Those Doing Upgrade to Legacy Systems with Metasys by Johnson Controls
- Specific Advice for Those Doing Upgrade to Legacy Systems with Metasys by Johnson Controls
- CAS BACnet Object Monitor – SubscribeCOV
- USA Tax Deduction and Credits Expires Jan 2014
- Amazing Computer Technology
- Engineering Failed
Managing Risk for Integration with Legacy Field Equipment
Are data trunks that connect field elements in spec? Are they overloaded? It is risky to assume the existing system is working perfectly – users may have learned to tolerate all the failures. If your job requires you to work with existing trunks you should:
1. Validate the trunks electrically
I.e. Measure voltages on a RS485 trunk. A set of rules or specification or even a test device can tell you whether the trunk is operating at the correct voltages. This should be done with a scope or if you are using a meter it should have a very fast response time and ideally have a latching function so you can note the maxima and minima. Short duration voltage events can affect data transmission significantly.
2. Validate the trunk against your project criteria
How many devices to plan to have on the trunk after the project? Is this within the operating limits of your technology choices?
What are your maximum and minimum response times? They may be significantly different from when the original system was installed and perhaps you cannot achieve your bandwidth requirements without breaking a trunk in two.
Can the upgrade system still cope with single point of failure inherent in serial trunks?
Ground potentials between the new building wing and the existing building.
On Ethernet systems you need to ensure you do not often exceed 67% of the total bandwidth. You should measure the existing usage and consider your additional load.
3. Validate the trunk against the technologies’ specification
These are the kind of things you need to evaluate.
Max then for RS485 is 4000 ft at 19200 baud. Do you intend pushing the speed up?
Unit load on RS485. System can handle a max of 32 full load 485 devices.
Are you adding 4 wire devices to a 2 wire trunk?
Does the installed trunk have a common conductor? You may need it for some devices if you are adding devices to a trunk.
Are parity settings of new devices compatible with parity settings used on existing devices?
If your upgrade project requires that you leave an existing building level controller in place and that your new controller to the system, there are several risks you need to manage.
When the new system sends a command or changes a set point the change can be overwritten by the old system. It’s possible that your command will be overwritten by logic in the building level controller or even logic in a field devices such as a DX9100.
Without inspecting the logic of the field device or the building level controller you cannot tell if this can happen.
It’s also possible that these ‘overrides’ from the existing system can be manually triggered by a user sending data from a GUI / Operator Workstation.
Where systems protect humans and equipment you should complete this investigation before making the system live. Learning the hard way is often learning the most expensive and reputation destroying way.
Often you will need to hire a consultant to make this evaluation for you since you and your team don’t have expertise in the legacy system you are upgrading. Allow some budget for this. This same consultant can also validate the legacy drawings you’ve been given against what is actually being controlled and used.
Red lines show sources of command contention.
A=Field Controller logic and schedules overwrites outputs / setpoints
B=Legacy Building Level Controller logic and schedules overwrites outputs / setpoints
C=Legacy system operator work station sends schedules and commands
D=New Operator stations send commands and schedules direct to field devices
E=New Building Level controllers send commands and schedules direct to field devices
Equipment list. The ultimate project reference for how items are tagged, named and known.
Valid backups of controller logic and documentation files.
Valid backup of work station / operator interface – screens, trends, controls screens, points being alarmed.
Control System Operations Manual.
Control System Drawings.
System to System Block Diagram – The automation system might interact with other systems such as the fire, evacuation, reservations, scheduling, security systems. These interfaces need to be well understood.
Bug List. The existing system may be operating incorrectly. You should not be reproducing controls that do not work well.
Some ways of programming minimize risk. Use of subroutines, use of templates and of macro’s reduce risk.
A huge and common problem on projects that relate to the so called Equipment List – the list of all devices, their names, tags, labels… As you work on a project and do programming you have to name and number devices, allocate addresses, make objects and variables and name them, do floor plans, place animated objects on floor plans, make trends and logs, alarms… To do this work you have to refer to the Equipment List (or Drawings). How often does this change? Often enough on some projects to ensure that a significant portion of the project effort is just keeping up with the changes.
If your project involves replacing another vendor’s building level controllers with your own, and re-using installed field level devices then you may need some extra help.
Does your team have all the skills required to evaluate the existing system and work with it during the changeover?
Until your own team has enough experience with the other vendor’s equipment you may need a specialist to provide the help and mentor a member of your own team on this foreign technology. For example, say you were doing an upgrade on a Metasys by Johnson Controls system. Do you have a team member who knows how to inspect the logic inside a Metasys controller? Do you have a team member who knows how to evaluate the existing data trunks? Do you have the software tools to open Metasys programming and label files?
Your purpose is to develop those skills within your own team to reduce cost in the long run. This can be achieved by having a consultant help with a specific project and at the same time transfer some of those skills to your own team.
There are times when it is extremely beneficial to pay for outside help. Probably the best time, is the period where you are developing your bid because then you can draw on the consultant’s experience to not only solve problems but evaluate the quality of the system you are upgrading and the quality of the documentation and programming that you may have to work with. The best practice is to use the consultant as a mentor to one of your own team members and make Technology Transfer part of their scope of work.
It also means that perhaps the new field tech you hired can be re-purposed. They worked for another vendor before this job, didn’t they? Instead of making your main focus getting the new hires up to speed on your own technology, use them for these legacy upgrade projects. Hire wisely. Compliment your team by drawing on the expertise of your vendors.
You may need to purchase the interface modules, connectors and software required to program, document the system you are upgrading. You can’t always expect the customer to have or provide these. If you use an outside consultant to evaluate the existing system you can ensure that they have all the tools to open all the system files, export labels and documentation, edit existing controller logic etc. The other route is to spend some money and purchase them for your own team. You are not only investing in the productivity of our own team, you are also making a statement to your customer about your professionalism.