Most PLC’s needed to be programmed via RS232 leads !!!.
#LOGO 8 FS4 POWER ON TIME SOFTWARE#
Development software for the “better” PLC’s was £150 or more. Most PLC’s were 12V or 24V powered, not mains, thus a 12/24V power supply would also be needed. However back then there were major issues with PLC’s, as far as I was concerned, that put the PLC controller project on a back burner: Also I started suffering failed timers as well, luckily failed to work so no damage done. I kept having the feeling there must be a simpler, more reliable way of controlling the electrics. I had converted my tank to high tech and pretty soon was messing around with 6 or more time switches, lights, CO2, power head, air pump, macro dosing, micro dosing and liquid carbon dosing.
I first started looking to use a PLC in around 2012. But compare this to buying the much more inconvenient time switches at say £10-£20 a go. A PLC will cost around £100, further I/O module another £100 and development software, if required, £40 odd. Timeguard still make & sell timers, which are highly regarded but cost £25 each.Īlso bear in mind, cost. My most reliable time switch, I bought early 1990’s, was in fact a UK made one, by Timeguard and still works. Luckily as fish are not affected by high nitrate and phosphate all was well. I ended up dumping 1litre of macro EI solution into my tank, when my dosing time switch failed to turn off after 15minutes. Also I have also confirmed that the words “wireless” and “reliable” do not occur in the same sentence, I have had sockets working for years then randomly one day, fail to turn on (or off). I have also experimented with wireless controlled mains sockets, nice as you can get many sockets in a small space, but I have had a few socket failures, where they no longer respond to the wireless commands. OK for air pump, no damage done, but I had a time switch fail to turn off and dumped a large amount of liquid carbon into my tank, killing both plants and fish. More dangerously for fish keeper, fail to turn off at end of time period or jam on. Sometimes fail to turn on for their time period. Their internal batteries run flat, so after a power failure they don’t retain their settings. Very commonly, just reset to 00:00 and loose all their time clock settings. Over the years I have had time switches that I have been through so many mains time switches on my fish tank, all failing in one way or another after a couple of years use. Siemens for instance quote a lifetime of over 100,000 hours for their devices and relay switching operations rated at over 3 million operations. PLC’s are industrial control electronics and are built from components that are in a completely different league of reliability compared to the components used in most mains time switches, that all now seem to originate from China. Main reason, in one word, is reliability. Why should I use a PLC as opposed to time switches ? This PLC also has an Ethernet interface that can be used to program upload & configure, as well as remotely monitoring its operation, so no manufacturer specific (ie expensive) programming lead are required.įigure 4 Siemens Logo! PLC and Expansion Module Note this is Logo!8 series, the older models Logo!7 and earlier PLC’s are not equivalent. This setup gives 12 relay switched outputs and mains level 16 inputs. This is a 230V (and 120V) device and can be used directly off the mains supply. It is connected to an expansion module, the module on the right, with a further 8 inputs and 8 relay outputs. The module with display on the left of the picture, is the main PLC with 8 inputs and 4 relay switched outputs. I thought the programming bit would be complicated but upon investigation the actual programming was very easy and quite simple.īelow is the PLC (and expansion module) I am using and will be describing are Siemens Logo!8 series. The ability to wire up mains electrics safely is required, if you can strip wires and wire a 13A plug correctly you are probably OK.Īs well as wiring in its simplest form a PLC will require some setup/configuration, not really programming per se, but will require configuring of timers and outputs.
Unfortunately using a PLC is not really a standard off the shelf solution, DIY construction, wiring, setup and programming is required. This article is mainly concerned with diagram 1, I will leave it to others to implement the other two diagrams. It also measures the pH (and temperature compensates the pH probe) and turns on enough CO2 to give a pH drop of 1 unit, giving 30ppm CO2. The PLC measures the water temperature and turns heater on and off at desired temperature. Water temperature and CO2 ppm controller.
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