Level and temp control lab.

Dear All,

I am developing an application in our company lab for training purpose,
My PLC contains 16 DI,12 DO , 4 AI and 2 AO.

Please find the attached drawing to see what i am actually making.

I need the suggestions of the seniors to improve or add some more important features.

I also want to add pressure related instrument,any suggestions please.

Some obvious questions:

Heater have a permissive to run as long as LS-2 detects fluid?

Pump have a permissive as long as LS-4 detects fluid? Some pumps can be hurt trying to pump without fluid.

What pressures are important that you would like to monitor?

how you apply/implement the SAFETY for this system.

I also want to add pressure related instrument, any suggestions please.

Click to expand...

The highest pressure in your system will probably be in the line just after the pump (when the pump is pumping). That pressure will be dependent on the size of the pump and the line. But to get a more stable pressure, measure at the farthest point from the pump. For training purposes, the pressure should be limited to only a few PSI (5 to 10). You can use a pressure transducer with an output proportional to the pressure. Wire that to one of your 4 PLC Analog Inputs.

Your program should be designed to check to see that the solenoid valve is Open, before starting the pump.

Me I worry more about flow more then pressure in situations like this. If the pump does not have any form of pressure relief (like a high pressure return valve) and there is a clog in the line or a valve is accidentally closed it can kill most pumps. Therefore I place flow SWITCHES in the line.

A couple of years ago I made a pH adjusting system that measured pH and flow (with an analog flow meter) and used that to turn on one of two metering pumps. The main challenge there is getting the water-chemical ratio right before you try to meter it in.

what type of analog inputcards are used and same for analog output.
what type of pump is used?
RTD is good, but expensive to interface.
make a small diagram, and use it as a input output with buttons and lamps.
I use SubD25 connectors so it can be reused without rewiring of the complete thing.
so they can swap PLC or embedded systems.

It was a fun project

I used an Allen Bradley SLC 500 running 2 pH adjustment systems. The PLC uses a four input analog card with 2 flow inputs and 2 pH inputs. The PLC scales the inputs then utilizes....I think the function is called "Calculate." With it I run it through a couple of formulas to determine at what rate to run a metering pump. The restriction was that I couldn't cover enough of the pH range with my system. I could have easily covered the whole range if I batch treated but I wanted to treat it in line. I had to make a choice as to how acidic or caustic the water would be . So to correct for an acidic solution I used caustic soda at 12 pH and calculated how often the pump would need to pump. Likewise for the caustic condition I used a 2 pH solution. For the output to the metering pumps (4 of them - 2 acid and 2 caustic) I used a four channel analog output card. Basically if it is barely out of the acceptable pH range it does 2 pumps per minute or something whereas if the water is at the extreme it it does 60 pumps (for instance). I've never used an RTD...which is not my way of saying that it is bad. Around my plant we use Type J and Type K thermocouples. Usually we interface with temperature controllers although we do have two applications where we run it off a PLC. One is a counter pressure casting machine - lets call it a die cast machine. It uses a thermocouple input module to control the amount of power that goes to the coils on the furnace that keeps the metal liquid. The second application is a curing oven for a paintline. Most ovens - as I said - use temperature controllers. The person who designed this system wanted the PLC and the HMI to have absolute control of the temperature. The sad thing is we never use the function - we always run it at certain temperatures. The PLC uses an analog input/output card to read the temperature and then adjust an actuator.