Flow Sensors: Acceptable Variation in Measurement?

[d2mini]

I have the GHL flow meter and it's installed on my drain plumbing.
The drain plumbing is pretty large and I have it dialed back after the sensor, right before it goes into the sump.
It measures in liters per hour, and if I watch the numbers, it bounces around.
For example.... 2265, 2298, 2388, 2276, 2198, 2187, 2220, 2388, 2187, 2298, 2332...
These are numbers I literally just recorded over the past minute or two.
About a 200 l/ph swing. Seems acceptable to me, no?

 

[Brew12]

I have the GHL flow meter and it's installed on my drain plumbing.
The drain plumbing is pretty large and I have it dialed back after the sensor, right before it goes into the sump.
It measures in liters per hour, and if I watch the numbers, it bounces around.
For example.... 2265, 2298, 2388, 2276, 2198, 2187, 2220, 2388, 2187, 2298, 2332...
These are numbers I literally just recorded over the past minute or two.
About a 200 l/ph swing. Seems acceptable to me, no?

I would call roughly 10% pretty good. Especially when you consider that flow isn't going to be constant and will bounce around.

 

[mcarroll]

I have the GHL flow meter and it's installed on my drain plumbing.
The drain plumbing is pretty large and I have it dialed back after the sensor, right before it goes into the sump.
It measures in liters per hour, and if I watch the numbers, it bounces around.
For example.... 2265, 2298, 2388, 2276, 2198, 2187, 2220, 2388, 2187, 2298, 2332...
These are numbers I literally just recorded over the past minute or two.
About a 200 l/ph swing. Seems acceptable to me, no?

I may be misreading, but unless the flow meter is the same diameter as your drain plumbing (or larger), you're not gonna get a true reading – a smaller one will be restricting the flow.

Wouldn't you want this on your return pump rather than the drain anyway? (Same flow rate, but I suspect this is how it's intended to be mounted.)

 

[d2mini]

I may be misreading, but unless the flow meter is the same diameter as your drain plumbing (or larger), you're not gonna get a true reading – a smaller one will be restricting the flow.

Wouldn't you want this on your return pump rather than the drain anyway? (Same flow rate, but I suspect this is how it's intended to be mounted.)

It's basically the same size. Drain plumbing is 1.25" and flow meter is 25mm (1") fittings but a smaller body. Restriction is fine. As mentioned above i have to dial back flow anyway.
Can't fit it on my return line.

 

[mcarroll]

About what flow rate are you supposed to be getting in theory?

(Just curious why it won't fit on the return plumbing?)

 

[d2mini]

(Just curious why it won't fit on the return plumbing?)

As far as expected flow rate... I don't have one. That flow rate is fine with me.
I was just curious about the numbers bouncing around. I just go by the average.

 

[TheEngineer]

10% seems reasonable to me. You’re likely more concerned with large deviations,right?

 

[d2mini]

10% seems reasonable to me. You’re likely more concerned with large deviations,right?

Correct.
I just wanted to make sure what I'm currently seeing is "normal".
I figure turbulence going through the sensor is probably what's causing changes every few seconds.
I'd wager that if the diameter of the sensor and plumbing were identical, I'd see less of a swing.

 

[TheEngineer]

Is this lamanar flow through it? Any turbulence at all will throw it off I’m sure.

I think your insight is very true. It may just be the turbulence created from the bushing down to the smaller size.

 

[LobsterOfJustice]

Is this on a gravity drain line, with air in the line? If so, that’s much better than expected. Air in the line will really mess with the reading of most flow meters.

 

[mcarroll]

For example.... 2265, 2298, 2388, 2276, 2198, 2187, 2220, 2388, 2187, 2298, 2332...
These are numbers I literally just recorded over the past minute or two.
About a 200 l/ph swing. Seems acceptable to me, no?

I was being dense...we can use these numbers. You're getting "around 500 GPH". Even in 1" plumbing there's no significant friction in that size pipe from that much flow.

That said, GHL sells a 1.25" version from looking at the website...looks like the same sensor no matter what size, so maybe you can get the bigger housing from them for a minimal cost? It might smooth out the readings if that's of interest.

 

[ca1ore]

I have found, with the Neptune sensors at least, that upsizing the flow meter helps to reduce friction losses. In apex you just have to specify the flow meter size for it to read properly - imagine there would be something similar for GHL. I have found the apex sensors to be quite precise (the readings don't bounce around much) but that the accuracy is +- 10%.

 

[Brew12]

I have found, with the Neptune sensors at least, that upsizing the flow meter helps to reduce friction losses. In apex you just have to specify the flow meter size for it to read properly - imagine there would be something similar for GHL. I have found the apex sensors to be quite precise (the readings don't bounce around much) but that the accuracy is +- 10%.

Keep in mind that the flow in a return is more constant than the flow in a drain. Since this sensor is on the drain line I feel the fluctuations are to be expected.

 

[ca1ore]

Keep in mind that the flow in a return is more constant than the flow in a drain. Since this sensor is on the drain line I feel the fluctuations are to be expected.

Understood, however, I am running five flow sensors, two of which are on drains - and they are all quite consistent. OK, both drains are siphons, so less chaotic than one that might have an air/water mix.

 

[d2mini]

At least when I got this about a year ago, this was the largest one they had. Havent looked lately.
I knew I didn't need to measure up to 9000 l/ph but I got it for the larger diameter.

EDIT: Just checked, I'm still seeing the same 3 meter sizes with the largest having the internal diameter of 1".

 

[mcarroll]

At least when I got this about a year ago, this was the largest one they had. Havent looked lately.
I knew I didn't need to measure up to 9000 l/ph but I got it for the larger diameter.

I'm looking at the 9000 L/h model here:
https://www.aquariumcomputer.com/products/profilux-accessories/ghl-sensors/

I may be reading it wrong, but I think that model is 1.25" (whatever DN 25 corresponds to), whereas the other two are 1/2" and 1".

 

[Brew12]

I'm looking at the 9000 L/h model here:
https://www.aquariumcomputer.com/products/profilux-accessories/ghl-sensors/

I may be reading it wrong, but I think that model is 1.25" (whatever DN 25 corresponds to), whereas the other two are 1/2" and 1".

It is 1" ID, well, 0.98" since it is 25mm. Silly metric system makes no sense. :p

 

[Lasse]

DN 25 -> 1"; DN 32 -> 1 1/4". the mm system off pipes refers to outside diameter -> the tum system refer to inside diameter

@d2mini Is there a lot of bends and valves near the flow meter. Normally you want the meter have a couple of decimeters horizontal pipe before and after the meter - just to get a laminary flow. I have no experiences of GHL flowmeters but my general knowledge of these says me that its important with no turbulences and no air in order to get a stable reading

Sincerely Lasse

 

[d2mini]

DN 25 -> 1"; DN 32 -> 1 1/4". the mm system off pipes refers to outside diameter -> the tum system refer to inside diameter

@d2mini Is there a lot of bends and valves near the flow meter. Normally you want the meter have a couple of decimeters horizontal pipe before and after the meter - just to get a laminary flow. I have no experiences of GHL flowmeters but my general knowledge of these says me that its important with no turbulences and no air in order to get a stable reading

Sincerely Lasse

I have a minimum of 6" (15cm) either side of the meter.
Unfortunately it is what it is when working inside the stand. ;)

 

[erk]

What kind of flow meter is it? I assume paddle wheel or turbine. Doubt it is an elliptical gear flow meter. For the paddle wheel or turbine, the typical requirement is 10x diameter straight on inlet and 5x diameter on outlet. This is the standard recommendation I've seen on industrial level flow meters. You could experiment though. No extra fittings or any obstructions within this region. This ensures laminar flow thru the pipe. You must use smooth bore tubing and clean it out regularly to keep biofilm and such to a minimum or it will disrupt the flow. Or you could average the reading out of the sensor over say a 10 second period. This would be the easier thing to do.

Keep in mind that the higher the fluid velocity, the longer the straights will need to be. It becomes easier to disturb the flow and cause shocks and turbulence with high velocity flows. This leads to a trade off between large diameter and small diameter tubing. Sure, smaller means shorter straights, but since the fluid velocity is higher, you will need to accommodate this and increase from 10x and 5x lead in/out to maybe 15x and 7x or more. You will probably need to do some testing or find a datasheet/contact the original manufacturer of the flow meter to see what they recommend.