Back to "Series-Parallel Circuits" Chapter 5
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The Universal Ammeter below is tested using a DC Power Supply, External Ammeter, and a 270 ohm resistor. Four nodes can be monitored using a DC Voltmeter (not shown in the schematic). Six Faults can be inserted in the Universal Ammeter. Each fault is implemented with an increase or decrease in one the resistances R1,R2,R3 or Rmeter. Check your troubleshooting conclusions by clicking Answer button.
Rmeter is the resistance of the meter movement.
UUT = Unit Under Test (In this case the Universal Ammeter.)
Faults are only inserted into UUT.
Failure of meter will only be simulated by increasing Rmeter.
All resistors are precision + or - 1% resistors.
%FS = Full Scale
Though 1ma FS ammeter is analog it is displayed as decimal % FS.
Pegged indicates that meter exceeds FS by more than 5%.
Universal Ammeter Meter Movement indicates FS when 1ma flows thru it.
No readings are valid when DC Power Supply reads blank.
Range 3 position switch simulation is implemented by option buttons:100ma,10ma,2ma.
Universal Ammeter current = (%FS)(Range)
Ext. Ammeter Reading = Universal Ammeter Reading (for fault free UUT).
Meter movement may be assumed to be fault free since this lesson is about resistance not magnetism or mechanics. An increase in resistance could occur as a result of a cold solder joint. This will effect the amount of current going through meter movement. However, if meter reads 50% of full scale, then you may rest assured that .5 mA is flowing thru the meter movement.