How high, high speed input required?

I am starting to develop a project for a new control system for a solvent mixing system.

I will be using a Telemec HMI that is currently operating a monitoring system for the section after this mixing area. This is using the first comms port to a Micrologixs 1000 (DF1); I want to use the second port through DH485 to a second plc.

PLC choice from Micrologix range or PLC500. But cost to minimum (isnt it allways!)

32 Valves
11 Level switches
1 E-Stop (1st part hard wired, 2nd part of circuit to PLC for monitoring)
2 high speed inputs; I could multiplex this to 1 input as the flow meters never run at the same time.

My first problem is how "high speed" inputs do I actually need for the signal from my flow meters. The single pulses (1 channel) are theoretically up to 430Hz. I have scoped the flow meter during a normal flow and got this:



I can see the mark space ratio is short (about 10:1), so I assume I cannot just work from the pulse frequency. The pulses are 0.3mS each.

I have been trying to find out about the SLC500 high speed card, but that looks to be a single channel, and designed for encoders (ie 2 channel A and B).

I can see that I wont get away with a standard input with a minumum scan time of 1mS I would miss most of the pulses. The SLC500 card looks serious overkill!

Basically all I want to do is using recipies from the HMI batch different mixes of solvent into certain tanks as each level drops. EG. 5 litre batch from HMI, convert 5L to a number of pulses, subtract "x" amount of pulses to make "y" to allow for solvent flow after valve shut-off. Open valve and count pulses until count => "y"; then turn off valve...... and so on through all tanks.

There is a bit of cleverer stuff for detecting flow fail on one of the 6 solvents and water, this will then check which other tanks are not using that particular solvent and inhibit those from filling. This is one of the problems with the current system; should one solvent supply fail the entire fill sequence is aborted for the rest of the 11 tanks.

Can anyone give any pointers as to what I need to look for?

Thanks

For a SLC 500 you will need a 1746 HSCE, and yes it is a single input card designed for encoders but it will work fine with your flowmeter.

Another option would be to buy a frequency to analog converter and run an analog into your PLC, this might be more cost effective.

The MicroLogix 1000s that I have used have DC inputs and they have at least 1 high speed counter input that are rated up to 6.6 kHz. It looks like your pulse train is much less than that.

Also, if necessary, some pulse shaping could be done to make your pulses easier to catch.

I would also advise the use of noise supression on the valve coils (I.E. reversed biased diodes on DC or RC on AC).

Best Regards,

Bob A.

Cheers allscott, that was the card I was looking at, but at £250 it seems a lot. I am trying to establish if the high speed input on a micrologix 1200 or 1100 would suffice.

As for the freq/V convertor, I think it would be difficult to then calculate the amount of solvent; I am not bothered about the flow rate just the amount. I will get 400 pulses/litre (approx, dependant upon flow rate) ie 1 pulse per 2.5ml.

The MicroLogix 1500 model 1764-LRP controller has two RS232 ports configurable for DF1 and DH485, and supports two High Speed Counter circuits on the DC I/O bases that run up to 20 kHz.

The DC inputs are 24VDC, not 5 VDC, so you'll need to amplify those two input channels with a signal conditioner.

What are the voltages and current ratings on the other I/O devices you will be using ? That will help you select the proper hardware.

I better re-scope that output, looks like 17v. That should trigger a 24v input though.

Making up a table now for 1100, 1200, 1500 and SLC500 for what extension cards I would need!

Nightmare

As for the output loads, I always drive relays in my panel that I can change; rather than use the PLC's relays. SO I could just use the FET output versions if they are cheaper

Thanks everyone so far

Thanks for the clarification; I couldn't easily determine the vertical scale on that trace and was looking at the 5.61 Vrms.

Save yourself some effort and narrow your selection to the MicroLogix 1500 1764-LRP controller. If you need one DH485 port and one DF1 port plus two high-speed counters, that's the most economical controller.

I'd only recommend SLC-5/03 if you need to have online editing. MicroLogix 1100 and 1200 lack the proper two communication ports and only have one High Speed Counter circuit.

Ken Roach said:

Thanks for the clarification; I couldn't easily determine the vertical scale on that trace and was looking at the 5.61 Vrms.

Save yourself some effort and narrow your selection to the MicroLogix 1500 1764-LRP controller. If you need one DH485 port and one DF1 port plus two high-speed counters, that's the most economical controller.

I'd only recommend SLC-5/03 if you need to have online editing. MicroLogix 1100 and 1200 lack the proper two communication ports and only have one High Speed Counter circuit.

Click to expand...

Ken's suggestion is mostly the route I would take. The only thing I would do different is adding an Net-ENI card to each PLC. This way you would still have a way to plug in your Laptop for programing work without disconnecting anything from the com ports.

Note: You can find programing examples of how to use the High Speed Inputs in AB's knowledge base.

Thanks for the info Clay and Ken.

I have been calculating what expansion cards I would need to then price up the plc.

For clarification on comms:

MICROLOGIX 1000 -------(DF1)------HMI------(DH485)------(new plc)

The original project on the micrologix was kept as cheap as possible (whilst still using the HMI) so it was done using DF1 straight to the HMI's first com port. I dont really want to have to re-program the HMI to allow it to connect to the micrologix 1000 through DH485. The AIC's in UK are £150 each! Hmmm, but if I do can I then plug laptop into the AIC to check on the micrologix 1000?

I can get away with 1 high speed input (just use a relay to select which flow meter I want to count, they NEVER run together.

Also comms; I need 1 DH485 to communicate with my HMI. I would also like to be able to plug laptop in to monitor program whilst its running. You mentioned the NET-ENI card, is that the same as the Ethernet port on the Micrologix 1100? Anyone used one? WHats available on the webserver?

Can I use the ethernet port to monitor the plc program?

Micrologix 1100: PLC 1763-L16BWA; I/P 1762-1Q8; O/P 2 off 1762-OW16; DH485 - cheap interface cable
Total £748

Micrologix 1200: PLC 1762-L40AWA, O/P 1762-OW16, DH485 AIC unit
Total £752

Micrologix 1500: PLC Base 1764-24BXB, PLC 1764-LRP, O/P 1769-OB32, DH485 AIC Module
Total £920

SLC500: Far too much £

To me the choice looks to be between the 1100 and 1200.

This is an in-house job (and the 2nd half of my self learning HMI training too!) so I need to keep to a minimum cost, there is still a new bank of 32 valves to add to cost.

Still thinking.....

The pointers in here are much appreciated; you guys are great!

Is space a factor? If so, the ML1100 is the one to use.
(Personally, I would use the ML1100. More features, newer, and has more options for comms. You can make your own Web page, look at all sorts of available status, I/O, etc, even drive commands.
I have worked with all Rockwell types, and they all have a place.

ML1000's are good, cheap and have been around for years. (not expandable)
ML1200's are the 1000's replacement. (More functions, and expandable)
ML1500's are better, are more expandable and have lots of memory,HUGE in footprint.
ML1100 NEW, (about 2 years now) great little brick PLC for the money.
Expandable, has Ethernet (come on....that's what is current now)and has DH-485/Serial.
Hope this helped.

SNK said:

Is space a factor? If so, the ML1100 is the one to use.
(Personally, I would use the ML1100. More features, newer, and has more options for comms. You can make your own Web page, look at all sorts of available status, I/O, etc, even drive commands.
I have worked with all Rockwell types, and they all have a place.

ML1000's are good, cheap and have been around for years. (not expandable)
ML1200's are the 1000's replacement. (More functions, and expandable)
ML1500's are better, are more expandable and have lots of memory,HUGE in footprint.
ML1100 NEW, (about 2 years now) great little brick PLC for the money.
Expandable, has Ethernet (come on....that's what is current now)and has DH-485/Serial.
Hope this helped.

Click to expand...

Yes it has!
I was thinking of the 1100 myself, are there any examples online of what you can do with the webserver? Can you connect to the plc through the Ethernet port in the same way as you can through channel 0?

Thanks again everyone, for your input (and sorry for all the questions!)

timbo_uk said:

2 high speed inputs; I could multiplex this to 1 input as the flow meters never run at the same time.

Click to expand...

Not sure I'd paint yourself in the corner like this...In the industry I work in things change on a moments notice. I would usually regret limiting myself like this.

Just a thought,

Greg

Fair point Greg.

Looking at the controller spec, as long as I dont go for the 1763-L16AWA I have 4 high speed inputs (pulse catch).

Can anyone explain a "Pulse Catch" ? Its speced at 20kHz, so should be fast enough.

Timbo, you can communicate directly through the Ethernet port, or connect it to a network of others, then connect from your living room if you really wanted.

You do know that it has a built in LCD, correct?
I have programmed a few of them with very basic HMI-like designs, with OK, Start, pressure readings, etc. Really basic operation for the LCD, but at least it saves on having to connect with your PC to access data......

Full functioning Ethernet.

AB's website is giving me a mixture of information.
In the general info it says the ML1100 has ONE highspeed input; yet if you download the manual you see this:



All seems strange to me!