EdHubbell
Member
Hey all - I'm new to PLC programming. So new I wrote most of this post using 'PCL' the first time. I *think* using a PLC is the appropriate way to solve the problem we're trying to address, but I'm not certain. I've come up with a set of system components that I think will accomplish what I need them to do. As this is the first time I've ever assembled a PLC system, I'd like to get it right (or close) from the start.
I write code most of the time (.NET, mobile apps, etc), so I'm used to very few limitations and structure when manipulating inputs. PLCs seem very limited (and highly structured) to my eyes. I have a feeling they aren't nearly as limited as I think. I know I'm completely ignorant.
We have some tools that uses pumps to inject a solution into a water line. The pumps on these tools occasionally fail. I want to add a system to these tools so that if the output pressure of the pump goes below what it normally is when running a light will go on. I'd also probably like to monitor the input line pressure as well, just to make sure the suction from the source isn't outside of the normal range.
We need to insure that the pump is actually pumping at the flowrate needed. We'd use a flowmeter, but the flow is on the order of 2 to 20ml per minute. Flowmeters with that level of sensitivity really run into money.
These tools already have a DIN rail in them with a little extra space and a 24V supply. They can have up to 4 pumps per tool.
I'm thinking I'll add a PLC with 8 analog inputs so I can have 2 pressure sensors per pump. The pressure sensors will be 0-60 psig on the pump output side and -14.7 to 30 psig compound on the input side. 24v power, 0-10V output on each. I only have about 6 inches of spare DIN rail space, but I've already got a 24V power supply in there I can tap into. Audible siren too.
0) Best resource for an experienced computer programmer to start learning PLC?
1) Will most PLCs allow me to program it so the input and output pressures stay within a certain range? So maybe see a signal that says the pump is on, wait 5 seconds and then make sure the output pressure is > 10psi.
2) Can I dynamically set the range - For example, after a start signal comes into the PLC, can I measure the pressure fluctuations and dynamically set some limits around them? I'd like to do something vaguely statistical, like get the standard deviation of the output pressure measurement and make sure we don't have multiple readings outside 3 sigma... No mystery on how to make this happen with a full programming language.
The reason I need this is to detect strange failure modes, like perhaps an o-ring failure in the pump. The pump has a specified stroke length and rate. If the pump is running but running 'leaky' (stroke not pushing the specified liquid volume), I think we'd see that in the pressure differential between the input and output.
3) Can I independently monitor multiple pumps?
4) I'm looking at putting the system on 20 to 30 tools, so this is more of an OEM application than a one-off. If anyone has PLC suggestions for a compact reliable PLC, I'm all ears. I'm looking at the Omron ZEN-20C1DR-D-V2 right now.
5) I'm trying to figure out if a PLC is the right solution, or should I use something that's a bit more flexible in what I can code into it. I don't actually know what that more flexible thing would be. That more flexible thing sits on a DIN rail. What is the name of that more flexible thing?
Ideally, I'd have a system that measured all 4 pumps and learned what 'typical' conditions were, and would scream when atypical things started happening. All 4 pumps might be set at different rates and pressures. Pump failure might look like larger than normal changes in the output pressure, for example. If the check valve at the end of the system fails (or locks closed) that may look like something else.
Apologies for the length of this post. Any advice is appreciated.
~Ed
I write code most of the time (.NET, mobile apps, etc), so I'm used to very few limitations and structure when manipulating inputs. PLCs seem very limited (and highly structured) to my eyes. I have a feeling they aren't nearly as limited as I think. I know I'm completely ignorant.
We have some tools that uses pumps to inject a solution into a water line. The pumps on these tools occasionally fail. I want to add a system to these tools so that if the output pressure of the pump goes below what it normally is when running a light will go on. I'd also probably like to monitor the input line pressure as well, just to make sure the suction from the source isn't outside of the normal range.
We need to insure that the pump is actually pumping at the flowrate needed. We'd use a flowmeter, but the flow is on the order of 2 to 20ml per minute. Flowmeters with that level of sensitivity really run into money.
These tools already have a DIN rail in them with a little extra space and a 24V supply. They can have up to 4 pumps per tool.
I'm thinking I'll add a PLC with 8 analog inputs so I can have 2 pressure sensors per pump. The pressure sensors will be 0-60 psig on the pump output side and -14.7 to 30 psig compound on the input side. 24v power, 0-10V output on each. I only have about 6 inches of spare DIN rail space, but I've already got a 24V power supply in there I can tap into. Audible siren too.
0) Best resource for an experienced computer programmer to start learning PLC?
1) Will most PLCs allow me to program it so the input and output pressures stay within a certain range? So maybe see a signal that says the pump is on, wait 5 seconds and then make sure the output pressure is > 10psi.
2) Can I dynamically set the range - For example, after a start signal comes into the PLC, can I measure the pressure fluctuations and dynamically set some limits around them? I'd like to do something vaguely statistical, like get the standard deviation of the output pressure measurement and make sure we don't have multiple readings outside 3 sigma... No mystery on how to make this happen with a full programming language.
The reason I need this is to detect strange failure modes, like perhaps an o-ring failure in the pump. The pump has a specified stroke length and rate. If the pump is running but running 'leaky' (stroke not pushing the specified liquid volume), I think we'd see that in the pressure differential between the input and output.
3) Can I independently monitor multiple pumps?
4) I'm looking at putting the system on 20 to 30 tools, so this is more of an OEM application than a one-off. If anyone has PLC suggestions for a compact reliable PLC, I'm all ears. I'm looking at the Omron ZEN-20C1DR-D-V2 right now.
5) I'm trying to figure out if a PLC is the right solution, or should I use something that's a bit more flexible in what I can code into it. I don't actually know what that more flexible thing would be. That more flexible thing sits on a DIN rail. What is the name of that more flexible thing?
Ideally, I'd have a system that measured all 4 pumps and learned what 'typical' conditions were, and would scream when atypical things started happening. All 4 pumps might be set at different rates and pressures. Pump failure might look like larger than normal changes in the output pressure, for example. If the check valve at the end of the system fails (or locks closed) that may look like something else.
Apologies for the length of this post. Any advice is appreciated.
~Ed