Clip on amp meter questions

[Bob Johnson]

I am using a clip on amp meter to check the cyclone I'm building. I find that if I have the wire at the point where the two jaws meet I get the lowest reading. If I move the wire around in the circle the current reading increases - I can get up to 1 amp more depending on where the wire is. I borrowed a neighbors a while ago and his seemed to act the same way.

Is this a normal characteristic of these meters? What is the real amperage? Or is the accuracy of these meters plus or minus 1 amp?

[Jim Wolfe]

I am using a clip on amp meter to check the cyclone I'm building. I find that if I have the wire at the point where the two jaws meet I get the lowest reading. If I move the wire around in the circle the current reading increases - I can get up to 1 amp more depending on where the wire is. I borrowed a neighbors a while ago and his seemed to act the same way.

Is this a normal characteristic of these meters? What is the real amperage? Or is the accuracy of these meters plus or minus 1 amp?

Bob , when you use a clamp on amp meter you should have the wire between the two arms , the wire you are checking should be one of the two leads for the motor .

[Bob Johnson]

Bob , when you use a clamp on amp meter you should have the wire between the two arms , the wire you are checking should be one of the two leads for the motor .

Jim, I do have a single wire between the two arms and the wire is one of the hot leads for the motor. Why does the amp reading vary so much depending on where in the circle formed by the two arms the wire is positioned? Where should the wire be positioned for a true reading?

[Jim Wolfe]

Jim, I do have a single wire between the two arms and the wire is one of the hot leads for the motor. Why does the amp reading vary so much depending on where in the circle formed by the two arms the wire is positioned? Where should the wire be positioned for a true reading?

Bob do you hav ethe instruction manual for the unit you are using , I haven't experence the problem your talking about. Here is a instuction card from a Fluke meter if it helps. Or you can try their web site http://www.fluke.com[IMG]Untitled-1.jpg[/IMG]

[Mike Cutler]

Bob. you should attempt to have the wire centered in the "jaws" of the clamp on ampmeter. The meter is sensing the building and collapsing of the flux field of the AC current at 60hz. As the alternating current changes throughout the sine wave it disturbs the field of flux established by the clamp on meter. The more, or less this field of flux is "cut" or influenced by the AC current is directly propotional to the strength of the current field being measured. Things that can have an affect on measurement can include the location of the meter to other "Stronger" fields, i.e the motor. If you get too close to the motor with an inexpensive meter it can influence the reading, another thing that can affect the measurement is what you are seeing, the"sensitivity" of the clamp on meter itself.As you move the wire around in side of the jaws you are moving the AC current field of flux, thus disturbing more or less of the lines of flux generated by the meter, and giving you a different measurement. A deviation of +/- 1 amp is pretty large though, in the instruction manual you have is there any reference to "nulling" the meter or zeroing it? and is there any type of sensitivity adjust? that you can easily access. A "rough" quick check would be to put both of the conductors inside of the jaws, the meter should be reading "zero" due to the fact that the AC current sine waves will be opposite for each conductor. Again though this is a "rough" indication that the meter is funtioning. I realize that I didn't answer your question, but without seeing the meters involved and the testing it is hard to say what could be wrong.

[Bob Johnson]

I have found something thats seems to be the cause of my variable readings. If I spread the hot leads so that they are about 3 inches apart, the variation drops to about .1 amp - probably within the accuracy of the meter. Having the non-measured lead next to the jaws causes variations

Putting the jaws around both leads shows .1 amp with no variation.

Not what I expected, but does this make sense to you experts out there?

[Mike Cutler]

Bob. The results you are getting are believable. In my previous post I forgot to mention that another cause for what you were seeing would be attributed to the range of the meter itself. The greater the range of the meter the greater the error could have been for a given reading. It sounds as if you are getting a representative indication of current now. The .1amp with both leads inside the jaws sounds about right also, as I said before it was a "rough" indication of meter operation. The close proximity of the second conductor to the jaws causing erroneous readings is possible.On the more expensive meters there are shielding schemes and circuits to cancel out this problem. What are the amperage readings you are getting with the meter for the cyclone?

[Bob Johnson]

Bob. The results you are getting are believable. In my previous post I forgot to mention that another cause for what you were seeing would be attributed to the range of the meter itself. The greater the range of the meter the greater the error could have been for a given reading. It sounds as if you are getting a representative indication of current now. The .1amp with both leads inside the jaws sounds about right also, as I said before it was a "rough" indication of meter operation. The close proximity of the second conductor to the jaws causing erroneous readings is possible.On the more expensive meters there are shielding schemes and circuits to cancel out this problem. What are the amperage readings you are getting with the meter for the cyclone?

Mike,

I'm building the cyclone from Bill Pentz's plans with the 5HP Leeson motor and the Sheldon's 14 inch material impeller.

With no filters (my filters haven't arrived yet), no cyclone, blower inlet sealed I get 8.9 amps and with the blower inlet open I get 20.8 amps

With no filters, the cyclone mounted to the blower, my chip bucket on, and the cyclone inlet sealed I get 9.0 amps and with the cyclone inlet open 15.7 amps and with 25 feet of 6" pvc hose on the cyclone inlet I get 12.6 amps.

Bob

[Bob Johnson]

Mike,

I'm building the cyclone from Bill Pentz's plans with the 5HP Leeson motor and the Sheldon's 14 inch material impeller.

With no filters (my filters haven't arrived yet), no cyclone, blower inlet sealed I get 8.9 amps and with the blower inlet open I get 20.8 amps

With no filters, the cyclone mounted to the blower, my chip bucket on, and the cyclone inlet sealed I get 9.0 amps and with the cyclone inlet open 15.7 amps and with 25 feet of 6" pvc hose on the cyclone inlet I get 12.6 amps.

Bob

I've gone back and rechecked my readings for the last three measurements using my new method. They all appear to have been about .5 amp low. The new readings are 9.5, 16.3, and 13.1 amps respecitively.

Does anyone have a table that relates amps to CFM for this setup?