How To Design And Build A Small Controls Project
Today’s post is a response to frustration. Some times when dealing with potential customers you waste a lot of time trying to save them money. They may want you to cut corners, spend a lot of your time (for free) chasing down cheaper parts or resources, all the while not realizing that they are only hurting their own cause. A consultant I know has been working with such a customer for the past year or so, and has been asking me for methods of getting their projects done cheaper. This is the same consultant and his customer that I wrote this post about last September.
Anyway, I wrote an article about what it takes to put together a small controls project and sent it to him. This is why I rarely do project work anymore; he had asked if it was something I could knock out “in a few afternoons”, cheaply of course. He also asked if I knew of anyone else who might. My question to him: why would they want to?
Building a Small Controls Project
This document is intended to describe some of the requirements and skills for a small project. It helps explain why these kinds of projects can seem very expensive; it takes more time to do a properly executed controls project than you would think, and often the skills required to do even a small project are not found in the same person. CAD, wiring, design and programming are entirely different skill sets. Of course controls components aren’t exactly cheap either! Hopefully you will find this article useful whether you are doing a project for someone else or in your own plant.
1. Specifying Parts
Describe the project on paper with as much detail as possible. Identify requirements – and potential future/expansion possibilities – in the document. Determine availability of utilities such as pneumatics, 480v/120v power, CFM and amperage. This should provide you with enough information to determine whether you will need a PLC, individual discrete control components such as temperature controllers, timers, counters or an HMI. Remember, you may need a 24vdc power supply.
This is also where you create an I/O list if specifying a PLC. This can be a temporary document, but starting a spreadsheet for the project at this point is a good idea. Handwritten notes should be kept in a folder or binder.
Catalogs and online resources are useful for selecting parts. A lot of detail goes into building a control system and there are a lot of small components such as terminal blocks, labels, jumpers, different gauges and colors of wire, etc. If this is to create a proposal rather than for the actual project, these small components can be estimated for cost and selection can wait until later. Use your local vendors to help if you don’t understand the specifications.
2.Designing the System
This part requires some knowledge of electrical and mechanical design. Again, for a small project items can be sketched by hand to determine sizes, one-line diagrams can be created for determining electrical requirements. Graph paper can be useful for determining sizing of the enclosure. The Excel spreadsheet used in specifying the system can be modified as part of the documentation process. If possible, AutoCAD or an equivalent design software package should be used for electrical and mechanical drawings. Dimensions will be very important here and any work done in this preliminary step may end up being used in the final documentation.
3. Ordering parts
Procurement of parts may involve some shopping around. Of course price is important, but don’t spend too much time trying to save a few pennies. Remember, time is money! Lead time is also an important consideration.
It is important here to keep all documents and paperwork for received components. Some of this may end up in the project binder, and packing lists can be used to reference purchase orders and possible returns later. Open boxes carefully and keep all packing materials for the same reason; some vendors won’t take components back unless it is in the original packaging.
4. Building the System
There are a lot of skills and tools required for wiring, panel fabrication and bracketry. Among these are panel layout (drilling, tapping, “pinging” drill points), panel prep (cutting of din-rail, wireway and component cutouts), wiring (Ferrule crimping, wire stripping and labeling), possible millwork and painting. There are also legal requirements that must be met for wire sizing, grounding and cabling/conduit outside the enclosure (field wiring). It is also often not economical to purchase some of the tools and components needed for proper panel fabrication, especially if you are doing a “one-off” project. It is often best to use an outside panel shop or electrician for this step. If the panel must be UL listed you may have to do this anyway. Also, without experience in this field, your system may not look very good; if it is going to a customer they may judge you by your work.
5. Programming and Software Design
For systems involving a PLC or HMI, knowledge of the platform’s software is required here. This software can often be quite expensive also, this should be taken into account during the specification design phase. Will your customer have the software? Is there an additional yearly licensing fee involved? Is there local support for troubleshooting or modification, or can the customer do it themselves?
Also, just because someone has done some PLC maintenance work does not mean they are a programmer. Even with years of experience, there are a lot of considerations that should be taken into account for maintenance and operator usage. HMI design is a bit of an art, as is PLC programming. As always, documentation is also critical. There should be LOTS of diagnostics, messages and faults programmed into a properly designed and programmed system, downtime costs money.
6. Startup and Debug
Most experienced programmers know not to worry too much about small mistakes during the programming and software phase, they will be discovered and fixed easily after the system is powered up. This is where the system gets fully tested before going into production. For larger systems, there is often a testing phase at the factory (FAT or Factory Acceptance Test, your shop) and another at the customer’s location after it is installed (SAT or Site Acceptance Test, final location). These events take up to two weeks each in some cases.
-Frank Lamb, April 16, 2018
Automation Consulting, LLC