I can't understand this meter
I can't understand this meter
(OP)
Hi
I need help understanding this ammeter that I recently came across in a hospital. See attached picture. The unit is old (mid 70's) so it is almost impossible to find any useful info online. The meter is connected to a main switchboard rated at 1600A. As far as I understand, the white needle indicates what the max allowed current is while the red needle indicates what the actual reading is. So if the red needle crosses the white needle some sort of alarm probably goes off and a breaker trips. However, what are the smaller numbers on the gauge supposed to indicate? These are all exactly 1/2 of the larger ones. This probably has something to do with the amp=3/6 but I don't understand what that means either. Also, what does the smaller meter indicate? It says AC amperes on it but I know that all the current in this switchboard is AC. The smaller needle also occasionally has small movements while the larger ones remain stationary. Anyone here come across something like this before? Any help would be greatly appreciated.
I need help understanding this ammeter that I recently came across in a hospital. See attached picture. The unit is old (mid 70's) so it is almost impossible to find any useful info online. The meter is connected to a main switchboard rated at 1600A. As far as I understand, the white needle indicates what the max allowed current is while the red needle indicates what the actual reading is. So if the red needle crosses the white needle some sort of alarm probably goes off and a breaker trips. However, what are the smaller numbers on the gauge supposed to indicate? These are all exactly 1/2 of the larger ones. This probably has something to do with the amp=3/6 but I don't understand what that means either. Also, what does the smaller meter indicate? It says AC amperes on it but I know that all the current in this switchboard is AC. The smaller needle also occasionally has small movements while the larger ones remain stationary. Anyone here come across something like this before? Any help would be greatly appreciated.






RE: I can't understand this meter
The two pointers (red and white) are probably thermal and react very slowly to the current. Such movements are usually bi-metal type with a heating winding. Very much like thermal protection in classical motor starters.
Such movements usually have a rather long time constant. Fifteen or thirty minutes are common. That corresponds to thermal time constant in many components like small generators and transformers and traces the temperature of those components in a rather crude way.
It is very probable that the white pointer is nothing but a peak indicator that is being dragged upscale by the red pointer to indicate what the maximum thermal load has been since last reset. I think that Bill (Ross, that is) has a very good idea about this instrument.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: I can't understand this meter
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Alan
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"It's always fun to do the impossible." - Walt Disney
RE: I can't understand this meter
Follow alehman's link for more information.
The needles on an alarm meter look similar, but there would be an obvious means to set the alarm pointer if this was an alarm meter.
As for the two scales and the 3/6 amp note; This is common on meters for dual voltage generators.
I agree with Skogsgurra's and alehmen's comments.
Bill
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"Why not the best?"
Jimmy Carter
RE: I can't understand this meter
Notice the little wire coming across near the letters "ADF" on the meter face: that's your maximum demand pointer pusher, connected to the reset lever at bottom center.
RE: I can't understand this meter