Magmeters flow errors

[Roy Matson]

Yes, they may have been working perfectly but now you say they read high. I told you why I think they are. I have installed a meter flowing down in continuious service, The meter is very noisy which I put down to entrained air.
Look at the installation recommendations. I bet it will have a big X beside your installation.
If you want to PM me I may be able to help further
roy_matson at yahoo dot ca
Regards
Roy

 

[curlyandshemp]

Air bubbles will effect but these meters have worked well in the same setup for a year.

The milk is not flowing continuously and is released in batches.

The probes and at the bottom end of the pipe and hence the probes are always dipped in milk.

The meters have plastic pipes on both sides.The meters are not grounded.

If they need to be grounded will they require grounding on both sides or only on one side of the meter.

You have been operating the meters outside the manufacturers recommendations. That fact it worked in the past is pure luck.

Flow tubes need to be flooded in order to work properly. If you get a flow meter rep to your site, they will state the meters are not installed properly. Until they are the rep cannot help you.

When looking for a problem, you need to eliminate the obvious. And in your case, the obvious question is "..are the meters installed properly?"

 

[plcsoftvsd]

Thanks Curly, for your advice and concern, actually i too was suspect of the installation, but if you see the probes they are at the btttom side of the cross section of flowmeter and is in shape of a slit. The milk is always covering the slit even at 60 deg angle and the flow is measured by the velocity of milk flowing in the slit.

I appreciate the air entrapment concerns, and i will see whether it can be eliminated.

What about the grounding of flowmeters, do i need to ground them on both sides?

cheers.

 

[danw]

There are various means, flange rings or grounding straps, of grounding (earthing) the mag's tube to achieve "potential equalization", depending on the style flow tube used; I suspect you're using a sanitary flow tube, but maybe not. You should refer to the manufacturer's installation guide for recommended practice.

Siemens makes these comments in its installation guide:

To obtain optimum results from the measuring system, the chassis body of the sensor must have the same electrical potential as the liquid being measured.

(It shows various grounding techniques for various model tubes/sensors. For the model 1100 sanitary flow tube it shows the graphic and the comment)

The sensor must be installed between two adapters. Potential equalization with the liquid occurs automatically via these adapters and through the adjacent pipe.

(in the service section of the manual)
Often problems with unstable/wrong measurements occur due to insufficient/wrong earthing or potential equalization. Please check this connection (first before proceeding with the troubleshooting check list).

Do you have remote mounted electronics? Does your model require grounding between the remote mounted electronics and the tube through a conductor in the multiconductor connecting cable, or just earth grounding?

 

[curlyandshemp]

Thanks Curly, for your advice and concern, actually i too was suspect of the installation, but if you see the probes they are at the btttom side of the cross section of flowmeter and is in shape of a slit. The milk is always covering the slit even at 60 deg angle and the flow is measured by the velocity of milk flowing in the slit.

I appreciate the air entrapment concerns, and i will see whether it can be eliminated.

What about the grounding of flowmeters, do i need to ground them on both sides?

cheers.

You mention the milk is flowing through plastic pipes?
Is this for human consumption?
Plastic piping is not sanitary. In Canada, the US and I am sure the rest of the world, dairy products must be conveyed through 3A stainless steel piping.

 

[plcsoftvsd]

Curly,
The milk is flowing through SS316 piping all around, it is the 400 mm length on both sides of the meter which is made of food grade plastic.

Danw,

I appreciate your point of earthing.

 

[Roy Matson]

This is an interesting thread, you mention a slit, could you post us a sketch?
I think grounding would only help if your signal was noisey. The pipe either side is stainless so the milk should be well grounded.
As I mentioned before I have experienced a problem with vertical down even though there is very little possibility of air entrainment.
I still think you have a slug of air filling part of the tube which causes the velocity of milk in the remaining area to flow faster thus give a false high flow rate.
Make sure you keep us posted on your findings
Thanks
Roy

 

[leitmotif]

Several plastics are FDA USDA approved for food. Tygon is one that comes to mind. Heck they use it for surgical.

If his sensor body is approved he is OK with that criteria. If it is plastic then for sure I would have the metal sensor body bonded to the stainless on both inlet and outlet sides - probably best to ground it also.

For air bubbles I would consider making sure that temporary couplings on suction side are vented thoroughly and for sure make sure no air leaks on pump suction side. I would have a high point to use as air vent when first starting. I would double check the pump suction side seals.

What really amazes me is OP has made no mention of factory manual or factory recommendations for mounting. I would surely be looking thru the manual to make sure sensor was installed correctly. Seems to me the factory should know a thing or two about their product.

Dan Bentler

 

[Lancie1]

Speaking as an old farm boy who has milked many cows the hard way, the white stuff comes out of the udder with air in it. Have you ever had air in your stomach? A cow has four stomach chambers to contain air. If you milk a bucket full, it will have air-entrained foam on the top 2 or 3 inches of the bucket. Heck, if you just sqirt some milk out of the tit into a cup, it will have foamy bubbles. I doubt if it would be possible to get all the air out of cow's milk without letting it sit for a long period of time in an open container (which I bet is a no-no for sanitation purposes). Some milk from different cows may have more or less, depending on what they are eating, and how healthy they are. After all these are live animals, not milk factories.

The best way to monitor how good of a job the milkers are doing cleaning the teat ends is to wipe the teat ends with an alcohol pad prior to unit attachment. Often times, the teat walls are very clean, however, the teat end is still covered with manure. The teat end is the most important piece of real estate on any dairy operation.
Once the teats have been properly cleaned, the units need to be put on the teats with as little air admission as possible. The more air that is leaked in during attachment, the more irritation there is to the udder and milk quality can suffer. If properly trained, 95 out of 100 teat should have the teat cups put on without any audible air leaks. I understand this is being picky, however, it does make a difference in the total milk quality program.

 

[curlyandshemp]

Speaking as an old farm boy who has milked many cows the hard way, the white stuff comes out of the udder with air in it. Have you ever had air in your stomach? A cow has four stomach chambers to contain air. If you milk a bucket full, it will have air-entrained foam on the top 2 or 3 inches of the bucket. Heck, if you just sqirt some milk out of the tit into a cup, it will have foamy bubbles. I doubt if it would be possible to get all the air out of cow's milk without letting it sit for a long period of time in an open container (which I bet is a no-no for sanitation purposes). Some milk from different cows may have more or less, depending on what they are eating, and how healthy they are. After all these are live animals, not milk factories.

Thats why in dairies when raw cream is received, it goes through an air eliminator before metering.

 

[curlyandshemp]

Curly,
The milk is flowing through SS316 piping all around, it is the 400 mm length on both sides of the meter which is made of food grade plastic.

Danw,

I appreciate your point of earthing.

If that is the case then, a ground strap should be connected from the stainless piping to the flowtube body.

 

[danw]

I suspect that the factory assumption for sanitary flow tubes is that the sanitary clamps form the grounding from the flow tube to what is assumed to be stainless steel piping, based on Siemens statement, "Potential equalization with the liquid occurs automatically via these adapters and through the adjacent pipe."

If your flow tubes mate to plastic piping, which are not conductive, it raises the issue that the errant flow rate might be a grounding issue.

Can you run, like Curlyandshemp suggests, a grounding strap between the flow tube and the piping on a couple of errant meters to see if that changes the response?

 

[plcsoftvsd]

We tried the ground strap,and didnt help.

The meters are being sent back to supplier.

Thanks everybody for inputs.

cheers.