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### Topic: Relation between PWM/flowrate (Peristaltic Pumps) (Read 1 time)previous topic - next topic

#### siva_dashq

##### Jun 18, 2013, 11:27 am
Hi everybody,

I need to control liquids flows in the context of my work experience.

I have a Arduino Mega 2560, 3 Ardumoto shields and 5 peristaltic pumps (80rpm) : http://www.thermoscientific.com/ecomm/servlet/productsdetail_11152_L10393_81880_13106372_-1

I'm using the PWM pin's in order to control the flowrate, and i wasn't able to find out on the internet whether the relation between PWM and flowrate is linear or not.

For now, i'm assuming this : flowrate range is 0.100 to 11mL/min, so :
analogWrite(PUMP_1, 255); //leads to a maximum flow rate
analogWrite(PUMP_1, 0); // leads to the minimum flowrate which is 0.1 ml/min
analogWrite(PUMP_1, 128); // leads to half of the maximum flowrate
etc etc.

Am i right or not?
If not, is there a graphic i can find to do a correct conversion of what i want?

#### Erdin

#1
##### Jun 18, 2013, 12:38 pm
It is not linear, there is no relation and there is no graphic.
It depends on the way the motor and the pump is build and the force needed and some on the PWM frequency. You have to measure the flow for the different PWM values. You could make a table with those values and let the Arduino convert the values.

With a good quality motor, the speed is more than the half at 50% PWM.
With some motors they start rotation at 30% PWM.

#### siva_dashq

#2
##### Jun 18, 2013, 01:25 pm
Ok so i have to take a day to test different pwm values and wrote down the associated flowrate.

Well i'll do that then... Kind of boring but i guess i have no other choice!

Bye and thanks for the answer

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