Thursday, December 03, 2015

Measuring water flow using TmallTech Hall Effect Sesnors

I have installed a Geothermal system and wanted to make sure that i am using it in an efficient manner.

The system engineer did not install the necessary monitoring tools, therefore, i wanted to find cheap and easy to use Flow meters. I search on Amazon and found about a suite of devices provided by TmallTech.

It was not a plug and play setup because in order to do the calculation correctly, you need some manufacturer information.  I was disappointed that the manufacturer did not send any data sheet about the product.  I googled such data sheet to no avail.  The piece of information that you would need is called the K factor.  the K factor lets you convert the pulse that the hall effect sensor to flow.  The K factor depends on the device and its diameter!

After lots of research and calibration, i arrived to a suitable solution

First  You need to read the Hall Effect sensor reading.  for that you can do one of the following

1) Buy a Digital Tachometer Gauge RPM.  A bought a good one from amazon called

DROK® 0.56" Digital Tachometer Gauge RPM Speed Measure Gauge Meter DC7~30V Tester Velocimeter 60-9999 RPM with Red Display for 14 USD ..

2) Use Arduino kit to connect the hall effect sensor to it and do a little bit of programming or googling

3) Use a reading device that is designed to work with hall effect flow meter. I bought one, but also it comes with no user guide and therefore , was not able to change the K factor to be suitable for the device i am using.  So I do not recommend this options

Actually, the first option proved to be the most accurate and viable option.  

By the way, you need a power source to supply both the flow meter and the Tachometer.

The entire success of the story depends on Knowing the K factor.

Below you can find the K factor for devices suppled by TmallTech

The following table will help you find flow meter reading from hall effect pulse rates

Pulse per Lit
Formula  frequency = K * Q(Lit/min)
Case Study, pulse/min
Flow lit / min
G2 inch
Pulse per min/60 =  0.2 * Q
Q=1200/60/0.2=100 L/min
G 1 1/2 inch
Pulse per min/60=0.5 * Q
Q=2700/60/0.5=90 L/min
 G 1.0 inch
Pulse per min/60=4.8*Q
Q=1800/60/4.8=6.25 lit/m
G ¾ Inch
Pulse per min/60=5.5*Q
Q=2000/60/5.5=6 lit/min
G ½
Pulse per min/60=7.5Q
Q=1600/60/7.5=3.5 lit/min

For example let us take the 2 inch case
Measuring the pulse rate using a device from amazon called
DROK® 0.56" Digital Tachometer Gauge RPM Speed Measure Gauge Meter DC7~30V Tester Velocimetry 60-9999 RPM with Red Display
The device measured 1200 pulse/min
The manufacturer specification is that the flow meter generates 12 pulse per lit
Therefore, the Frequency HZ (pulse/second) is 1200/60=  20 Hz
Therefore, the flow per second is  20hz/12 = 1.66  lit/second
Applying the formula above gives the same result
Q = pulse per min/60 / 0.2 è  pulse/second  /0.2 è pulse/second /12/60 è 20/0.2=100 lit/second
ð    100/60 è  1.6 lit/min

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