GE ultrasonic flow meter, how to connect?

Using Arduino Sensors
#1

I'm wondering the best way to connect this flow meter to my Arduino UNO. It is an ultrasonic flow meter with multiple outputs.

http://www.ge-mcs.com/en/flow/ultrasonic-liquid/aquatrans-at868.html

http://www.ge-mcs.com/download/sensing-manuals/910-218D.pdf

I have experience hooking up a 10 dollar flow meter.

The cheap model has voltage, ground, and a signal output. It can be powered with the arduino, and I connect the signal to pin 2 using interrupts. No problem.

The expensive model has SIG (+) and RTN (-) outputs for a 4-20ma line and SIG (+) and RTN (-) outputs for a frequency/totalizer line. It has it's own power line.

I'm assuming the frequency/totalizer line is the pulse line? I can feed the SIG(+) line into pin 2 and it would be like the pulse line like a cheap model? If so, do I just ground the return line? Would this be better than using the 4-20ma analog line?

No, I wish I could, but I cannot test this to confirm. I'm building this for someone who has the flow meter overseas, so I need to guess correctly the first time. I can make a few code changes after the fact, but I need to understand how to accept the output into the arduino before I send it.

#2

stoutfiles wrote:

so I need to guess correctly the first time

Don't guess when doing work like this. Research what you are doing and calculate it so it is correct first time. Guessing is like assumptions and only lead to frustration and errors.

Read up on 4-20mA current loop interfaces, they have been around in industrial automation for many many years.

Normally, if you wish to read a 4-20mA signal into a voltage based analog input, you would place a precision resistor across the loop to generate a voltage proportional to the loop current. Typically this resistor is a 250Ω resistor. This resistor needs to be or better than 0.1%.

With a 4-20mA loop, you will then have a 1 - 5 volt signal at your Arduino ananlog input.
4mA will develop a 1 volt drop across the 250Ω resistor.
20mA will develop a 5 volt drop across the 250Ω resistor.
And anything between will be proportional.

Also, think about any needed protection, especially if the sensor is mounted some distance away or is near other equipment that generates EMI.

Paul

#3

rockwallaby:
stoutfiles wrote: Don't guess when doing work like this. Research what you are doing and calculate it so it is correct first time. Guessing is like assumptions and only lead to frustration and errors.

Exactly. That's why I'm researching it and posting here for advice.

rockwallaby:
Read up on 4-20mA current loop interfaces, they have been around in industrial automation for many many years.

I agree that 4-20mA is a viable alternative, but at the moment I'd prefer to use a digital signal if it exists. I'm just confused why a digital signal would have a positive and negative line so I'm not exactly sure if this line (the frequency/totalizer line) functions the same as a digital line from a cheap flow meter. That's my main question; is the frequency/totalizer line a digital signal that can be measure in a similar format to cheap flow meters.

If I can't use a digital line, I will have to use the analog line, though I feel it might not be nearly as accurate.

#4

I agree that 4-20mA is a viable alternative, but at the moment I'd prefer to use a digital signal if it exists. I'm just confused why a digital signal would have a positive and negative line so I'm not exactly sure if this line (the frequency/totalizer line) functions the same as a digital line from a cheap flow meter. That's my main question; is the frequency/totalizer line a digital signal that can be measure in a similar format to cheap flow meters.

If I can't use a digital line, I will have to use the analog line, though I feel it might not be nearly as accurate.

Quite an elaborate flow meter (not sure what the Arduino is for). Anyways, all signals are accurate ... they're just best suited for different purposes.

An analogy of the three possible signals, Analog, Frequency, Totalizer would be Speedometer, Tachometer, Odometer respectively.

Why choose just one signal? You can have both analog and digital at the same time.

Analog is great for plots, data logging, setting alarm levels, analyzing useage patterns, etc.

With digital, you can choose Frequency or Totalizer. Both methods emit pulses on the same wire.

Frequency gives high resolution (0.1-10kHz) that could represent gal/min (flow rate) if you program it so.

In Totalizer mode, each pulse represents a certain volume as programmed. The pulse rate will still vary with the flow rate, but the frequency will be much lower. There is no loss in accuracy. Pulses can directly be counted (totalized) without any calculations required.

I've seen the cheap flow meters specified both ways ... volume per pulse or frequency per flowrate.

#5