DC ammeter - UK Vintage Radio Repair and Restoration Discussion Forum

ex 2 Base · 27th Apr 2018, 5:28 pm

I would like to make a Clip on type DIRECT CURRNET ammeter, has any one a circuit diagram or could some one point me in the right direction to obtain details etc. Ted

Herald1360 · 27th Apr 2018, 5:57 pm

You'll need a system for driving a winding on the clip on magnetic core so as to drive the field in the core to zero. You can then infer the current in the wire being monitored from the number of turns in the backoff winding and the current in it.

Detecting zero field is where it gets interesting. A simple hall effect device can be used, but the system will be a bit drifty and imprecise- probably OK for a percent or two accuracy.

Precision DCCTs (dc current transformers) use techniques such as flux gate magnetometry for the null detection- great fun!

Argus25 · 30th Apr 2018, 11:52 pm

I would suggest placing a Hall device like a UG3503U in the magnetic pathway of a toroid or other split iron core. Herald1360 is bang on about the drift. Although Hall devices themselves like the UGN series are in fact based on a bridge architecture, with an internal chopper stabilized OP amp, there is still drift. But I found a way to get rid of nearly all of the drift using a "double bridge method" An extra device is cheap. I simply use two of the UGN devices, one in the magnetic circuit and one outside it for drift cancellation.

Have a look at page 4 of this article in a regulator called "The Hybrid Hall" In your case, rather than using the two transistor differential amplifier you would just feed the two Hall outputs into an op amp's inputs to make a linear current meter.

http://worldphaco.com/uploads/HISTOR...CS_ARCHIVE.pdf

27th Apr 2018, 5:28 pm	#1
ex 2 Base Heptode Join Date: Nov 2009 Location: Scarborough, North Yorkshire, UK. Posts: 510	DC ammeter I would like to make a Clip on type DIRECT CURRNET ammeter, has any one a circuit diagram or could some one point me in the right direction to obtain details etc. Ted

27th Apr 2018, 5:57 pm	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: DC ammeter You'll need a system for driving a winding on the clip on magnetic core so as to drive the field in the core to zero. You can then infer the current in the wire being monitored from the number of turns in the backoff winding and the current in it. Detecting zero field is where it gets interesting. A simple hall effect device can be used, but the system will be a bit drifty and imprecise- probably OK for a percent or two accuracy. Precision DCCTs (dc current transformers) use techniques such as flux gate magnetometry for the null detection- great fun! __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

30th Apr 2018, 11:52 pm	#3
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: DC ammeter I would suggest placing a Hall device like a UG3503U in the magnetic pathway of a toroid or other split iron core. Herald1360 is bang on about the drift. Although Hall devices themselves like the UGN series are in fact based on a bridge architecture, with an internal chopper stabilized OP amp, there is still drift. But I found a way to get rid of nearly all of the drift using a "double bridge method" An extra device is cheap. I simply use two of the UGN devices, one in the magnetic circuit and one outside it for drift cancellation. Have a look at page 4 of this article in a regulator called "The Hybrid Hall" In your case, rather than using the two transistor differential amplifier you would just feed the two Hall outputs into an op amp's inputs to make a linear current meter. http://worldphaco.com/uploads/HISTOR...CS_ARCHIVE.pdf