I am planning a device to inject one of two additives into a variable flow of water achieving a relatively constant concentration.
My device will be used for wash down of a boat, engines and gear. It will be 12v battery powered, and used at boat ramps. Accuracy of dosing isn't critical +/-10% is no problem. However, water supply (L/min) at ramps varies by up to 50%, so a dynamic dosing system is required. I can't find a DC 12v metering pump that measures flow and adjusts dosing simultaneously. So I need to make one.
I've done my intitial research and I would appreciate some early feedback on the overall approach I have planned so far.
Code to determine required additive rate (ml/min) based on flow rate and target concentration
Code to determine pump speed required to deliver additive rate
Code to drive pump at required speed
If selector switch is at 0 do nothing
If selector switch is at 1 run pump 1 at required speed
If selector switch is at 2 run pump 2 at required speed
Loop
Most of the code is available from manufacturers or here. I'm hoping I'll just need to ad a few lines to work out additive rate and pump speed etc (simple maths) and link the various bits together.
What are you using to administer the dose of additive? I think it's not the RATE that's important. It's just about volume. For example, if you had a device capable of administering one drip of additive. And you need one drip of additive per X amount of water, you simply have to find out how many pulses you get from that flow sensor for X amount of water.
Your sketch would then be simple, Just monitor the flow sensor and update a counter whenever a pulse is detected. Once counter reaches the critical point just send one drip of additive and reset counter.
The pump can come prefitted with a driver that accepts 0-5vDC as a control signal, and a seperate 12v dc power supply. On that basis I believe I can provide control direct from the Arudino (no motor shield) using a PWM output and power the pump seperately from a 12vDC regulator.
I've also decided to control selection of Additive 1 or 2 with a manual 3 way valve, rather than electronically. That way I only need one motor.
Ken, the additive is being adminsitered by a vairable speed, perstaltic pump.
I need to deliver a stream of water with a constant concentration of additive.
The water is flowing at a L/min. The addtive need to be continuousy injected at a constant 0.5mL/L.
Therefore I need to inject additive at a rate that is (volume*0.5mL)/time.
As an example i the wate flow is 7L/min, I need to add 3.5mL each minute.
So .... I think I need to count flow meter pulses every X seconds then change additive injection rate (via PWM output to pump) to suit the flow rate. Then repeat.
But I am John Snow on this.
KenF:
What are you using to administer the dose of additive? I think it's not the RATE that's important. It's just about volume. For example, if you had a device capable of administering one drip of additive. And you need one drip of additive per X amount of water, you simply have to find out how many pulses you get from that flow sensor for X amount of water.
Your sketch would then be simple, Just monitor the flow sensor and update a counter whenever a pulse is detected. Once counter reaches the critical point just send one drip of additive and reset counter.
Dave, I'm planning on having a mixing chamber. This will be a 400mm length of 80mm pvc pipe with sealed ends. The angles and positions of the input nozzles, the output nozzle; and internal fins will ensure thorough mixing.
The perstaltic pumps will output 30mL minute.
The required additive rate is 0.5mL/L.
Therefore, one pump will dose 60L/min of water.
I reality I only need 20L/min so I will regulate incoming water pressure to allow a maximum volume (given the hose diamter) of say 25L/min. The pump will then run at approximately 40% capacity.
The flow sensor is rated to 30L/min so it will run at about 80% capacity.
dave-in-nj:
pump 200 looks nice. peristaltic is the way to go, just like commercial soap dispensers
some form of mixing inside of the pipe
then just run for a minute until the control settles and then fill a 5 gallon bucket to test %
you are on the right track !
have you done the basic calculations for GPM from the hose at maximum and the pump to verify the pump selection ?