Started programming my PLC

[perpetual98]

So I've had some PLC stuff sitting in my closet for the past year or so and just never had the time/ambition to use it. I busted it out last weekend and started playing around with it, now my brain is going overtime trying to figure out what else to try to make this little bugger do.

The unit is an Allen-Bradly Micrologix 1500 and I'm programming it with RSLogix 500. Anyone here have any experience with these products?

I don't have it set up yet on the tanks because I want to get all the ladder figured out first. I'm going to use it to control both of my tanks in the living room.

Currently I've got it set up to control the following:

The top-off systems on both tanks. When the sump level drops below the "low" switch, it toggles an output which opens a solenoid and fills the sump until the "full" switch turns off that loop. That was the easiest program rung to do.

It's also set up to do the lighting on both tanks, which consists of: Tank 1) 6 T5 bulbs (three different time settings) and two halides (one time setting) - Tank 2) 4 T5 bulbs (one time setting) and refugium light (one time setting)

My next step is going to be to try to figure out how to monitor/control temperature. I'm not real sure where to go from here. I was thinking that I could use a thermistor and the analog inputs, but I'm not sure that will work after doing some reading.

Eventually I want it to control the temperature, the ORP, monitor the pH, etc. I'm also going to try to play with a Panelview down the road too, so I've got some ambitious goals for the hardware.

If anyone has any experience with that sort of stuff, I'd love some input!

Eric

 

[slug]

One suggestion is to watch ebay for ph/orp transmitters. I've picked up a few nice ones for less then $25.

The unit I'm using has direct inputs fo thermocouples so tha's what I've using, you may want to seach ebay for a temp transmitter too.

 

[perpetual98]

I'll keep my eyes peeled. Do you have any more information on those transmitters? How do they interface with the PLC? I'm trying to figure out if I should get a thermocouple module for the PLC or and RTD module.

 

[perpetual98]

Maybe this thread should be moved to the R3CA forum so that it doesn't get lost. Maybe some more automation people will see it there.

 

[BeanAnimal]

That forum gets no traffic (or at least it didnt)

 

[perpetual98]

I hear ya Bean, but the DIY forum gets so MUCH traffic that this baby will be on page 7 come morning.

 

[H20ENG]

Slug,
Do tell of the transmitters! Thats my biggest dissapointment going the PLC route- pH and ORP measurement control are a tough nut to crack for me.

 

[perpetual98]

What would you guys recommend to get a temperature reading into the PLC? I'm thinking that a thermocouple module on the PLC along with a thermocouple in the sump. I saw some 304 Stainless thermocouples on the net for a decent price. Would those work? That's what one of the reef controllers used at any rate.

Eric

 

[FuzzyLogic]

One suggestion is to watch ebay for ph/orp transmitters. I've picked up a few nice ones for less then $25.

I'm currently bidding on a brand new PH/ORP controller/transmitter right now. I'll be happy If I can get it for less than $150.

 

[perpetual98]

I'm halfway through a huge thread here about PLC control. Seems that some people have made their own transmitters for around $10. I still haven't gotten to the schematic though. I'm a big fan of $10 as opposed to $150. I'll let you know if I find anything. My problem comes in that I'm looking to control multiple tanks and if I had to shell out $150 four times (ph and ORP on two tank) I'm just throwing money at something that should be cheaper. Heck, I can get Milwaukee controllers for way less than that.

 

[shouldabenacowboy]

I have worked with RSlogix 5, 500 and 5000 but I have never worked with a Micrologix processor. If you need any help programming let me know.......

Matt

 

[perpetual98]

Sounds good! So far, the programming hasn't been too bad, it's the hardware that I'm running into issues with right now. Any RSView / Panelview experience?

 

[JER-Z]

i work w/ SLC's, Micrologix, and have taken a Rockwell Training Course on RSLogix 500.

I am by no means a Programming wizzard, I am more into the commissioning/testing of allen bradley automated equipment. What kind of hardware issues are you having?

Edit: Just noticed the Controls Engineer two posts above me...Chances are, he will be more help. I still have all the training books on hand, let me know if i can be of any assistance.

From my experience, the most difficult part is getting everything communicating w/ eachother properly.

 

[perpetual98]

Ok, to put it bluntly, I'm about as green to the PLC thing as can be. I've managed to hammer out some Ladder, but that's about it.

Right now I'm after the hardware that will translate things like temperature, pH and ORP into something the PLC will understand.

For instance, I'm trying to figure out of a Thermocouple module or an RTD module would be better to add on to the PLC for temperature monitoring/control. I'm trying to do as much reading as I can, but sometimes that isn't nearly as valuable as someone who has the experience. I know for a fact that I can control temp with a PLC because we do it here at work. Now I just need to find out which way is the best way to go, oh yeah, and also find something (like a thermocouple) that will last in a saltwater environment.

Getting into things like pH and ORP control involve translating what the probe in the tank says to something the PLC can understand and do something with. I think I need to get a pH/ORP transmitter, but I'm looking for cheap, not fancy. If I can build it myself, I'd rather do that than spend oodles of money. I can just buy standalone hardware to do those things. Part of the fun of this project is having it all done in one device.

Eric

 

[FuzzyLogic]

Yeah, I've been through all the PLC threads here on RC. The homemade transmitter seem like the holy grail of cheap analog control. I don't think anybody put together something that was reliable enough. The item I am looking at is a transmitter AND controller. That's why it is a little more expensive. A unit like this normally cost $800. I want a dedicated controller for PH/ORP that can transmit 4-20mA to my PLC. The PLC will be used just for data acquisition. Of course the PLC will be used to control discrete data (lights, pumps, solenoids, ...)

 

[slug]

Watch ebay, I have 3 ph transmitters now and have seen more over the last few months cheaper then $30 each. Might have to wait a while, and don't bid them up too high against each other =P

Most likely the transmitters will be some type of current loop, meaning the output will be 4-20ma. I don't know what types of inputs you'll have, probably not milliamps in though so you need to convert the signal volts.

Stolen from omega.com:

"Most instrumentation is set up to receive voltage. A commonly asked question is how to use a current signal with instrumentation set up for voltage. This is simply done by installing a resistor across the input terminals of the instrumentation. The value of the resistor is determined by Ohms law (V = IR). For example, installing a 500 ohm resistor will convert 20 mA to 10 volts (V = IR = .020 x 500). This is shown in Figure 7. The only other consideration is the zero offset. Since most current loops have a low end of 4 mA, there will be a zero offset. Using the same value resistor as above 4 mA will convert to 2 volts."

 

[FuzzyLogic]

I stole this from a PLC programming website. Useful for scaling your analog imput.


For any unit conversion on any PLC you can use four function math with the following, which
asumes integer math:

DataOffset = Data in input register at 4 mA (or zero analog signal of whatever range
- for example 0 VDC on a 0-10 VDC transmitter)

DataSPan = Data at 20 mA - Data @ 4 mA

FACTOR = arbitrary factor (multiple of 10) needed to get proper resolution and accuracy

EU = Engineering Units x FACTOR

EUOffset = Engineering Units @ 4 mA x FACTOR

EUSpan = (Engineering Units @ 20 mA - Engineering
Units @ 4 mA) x FACTOR

DATA = Actual data reading in input register

EU = ((EUSpan x (DATA - DataOffset))/DataSpan) + EUOffset

ProcessValue = EU / FACTOR

For Example, 15-360 s/m from 4-20 mA with resolution of 0.1 s/m:

FACTOR = 10
Data @ 4 mA = 6240
Data @ 20 mA = 31208
DataOffset = 6240
DataSpan = 31208 - 6240 = 24968
EUOffset = 15 x 10 = 150
EUSpan = (360 - 15) x 10 = 3450

mA = 16.74
DATA = 18975
EU = ((3450 x (18975 - 6240)) / 24968) + 150 = 1908

Process Value = 1908 / 10 = 190.8 s/m

 

[perpetual98]

Yikes. I think I just realized that I'm in way over my head.

 

[aquaman49504]

I am using a micrologix 500 and will be using a panelview 550 for an interface. I only use it for the digital inputs, relay outputs, and thermocouple inputs. I thought it would be cool to use a analog card for sensors but got scared off, as I am unfamiliar with programming for them. Maybe in the future I will be using sensors but for now I am just using a Pinpoint PH monitor for its ease of use. I would be interested if someone knew how to program for various sensors.

 

[perpetual98]

Can you explain how you're using the thermocouple input? I assume it's for temperature monitoring/control?