chrisveitch Posted October 14, 2012 Share Posted October 14, 2012 I'm interested in using an ammeter to diagnose problems in 009/N mechanisms but I'm electronically pretty naive and would appreciate some advice. 1. Will a standard multimeter do the job for this function and if so, how should it be set up? 2. If not, can anyone advise on a suitable bit of equipment and how to set it up? Regards, Chris Veitch Link to post Share on other sites More sharing options...
'CHARD Posted October 14, 2012 Share Posted October 14, 2012 As I'm something of an ammeter in such areas, I shall defer to more learned colleagues who will be along shortly..... as well as Security Link to post Share on other sites More sharing options...
Blacque Jacque Posted October 14, 2012 Share Posted October 14, 2012 I'm guessing you're looking for indications of binding etc ? If so, a digital multimeter is not the best tool, especially cheap digital meters. In this case a conventional analogue needle meter gives a clearer indication of current trends. Most digital meters take samples around 2.5 times a second which cannot show the current peaks with any clarity. For simple current measurements the meter (whether analogue or digital) would be connected in series with the device under test. A meter handling up to 1amp would cover the range you need comfortably. A smaller range, say 500mA will give better resolution, but is at greater risk of damage if the mechanism draws excess current. Rapid Electronics sell analogue meters, but all only have a 250mA DC range as a maximum, but they are cheap enough: http://www.rapidonli...gue-Multimeters Maplin have a couple of analogue ones too, but again they only have a 250mA range (ok, so one has a 10A range, but that's completely useless for your intended purpose). http://www.maplin.co.uk/general-purpose-analoguemultimeter-25414 EDIT: Added Maplin link. Link to post Share on other sites More sharing options...
chrisveitch Posted October 14, 2012 Author Share Posted October 14, 2012 I'm guessing you're looking for indications of binding etc ? If so, a digital multimeter is not the best tool, especially cheap digital meters. In this case a conventional analogue needle meter gives a clearer indication of current trends. Most digital meters take samples around 2.5 times a second which cannot show the current peaks with any clarity. For simple current measurements the meter (whether analogue or digital) would be connected in series with the device under test. A meter handling up to 1amp would cover the range you need comfortably. A smaller range, say 500mA will give better resolution, but is at greater risk of damage if the mechanism draws excess current. Rapid Electronics sell analogue meters, but all only have a 250mA DC range as a maximum, but they are cheap enough: http://www.rapidonli...gue-Multimeters Maplin have a couple of analogue ones too, but again they only have a 250mA range (ok, so one has a 10A range, but that's completely useless for your intended purpose). http://www.maplin.co...ultimeter-25414 EDIT: Added Maplin link. Many thanks for that. I suspected that a multimeter would tell me something, but not much, and you've confirmed this. Thanks you for the advice on ammeter selection - at least I now know what to look for. Regards, Chris Link to post Share on other sites More sharing options...
stewartingram Posted October 14, 2012 Share Posted October 14, 2012 If you get hold of a meter (I got mine from a local electronics shop, old-fashioned variety, sadly disappearing just like model shops), you can add a shunt resistor to change its range. For model railway purposes on a controller, extreme accuracy is not that important, as we are looking for changes in current rather than an absolute value. I'm not aware of your skills here so apologise if I appear to be over simplifying things, but trust me this works. Mine is on the DC supply to a home made pulse width modulation (PWM) controller; I have used the dc i/p so as to get a smooth dc flow through the ammeter. As such it also shows the current drawn by the controller itself, but I ignore that. Looking at the diagram, Itotal is the current drawn by the motor (ie what you actually want to read with the meter). Ifsd is the actual indication at full scale deflection of the meter (ie a 500mA fsd meter will read 500mA). Rm is the internal resistance of the meter (should be marked on it). Rs is the Shunt resistor that you add to change the meter reading. The formula to use is Rs = (Ifsd x Rm) divided by (Itotal - Ifsd) Edit - just to confirm I am talking about a METER on its own - NOT a multimeter which are freely available. I would think a place like Maplins would sell individual meters, but at a price I would just laugh at. My last ones cost me pence from Gee's in Mill Road Cambridge about 5 years ago. Stewart Link to post Share on other sites More sharing options...
shortliner Posted October 14, 2012 Share Posted October 14, 2012 A possible answer to your question http://www.trainelectronics.com/Meter_HF/These meters are available with little problem in UK Link to post Share on other sites More sharing options...
Il Grifone Posted October 14, 2012 Share Posted October 14, 2012 Around £3 on eBay (even less direct from China). Analogue or digital as preferred. Link to post Share on other sites More sharing options...
chrisveitch Posted October 14, 2012 Author Share Posted October 14, 2012 Thanks for your assistance, guys. I now have a much better idea of what I need. Regards, Chris Link to post Share on other sites More sharing options...
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