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Current Monitors / Sensors / Detectors Circuits
Designed by David A. Johnson, P.E.

Last Updated on:
Tuesday, October 13, 2009 01:26 PM

Master Category List - Dave's Circuits

 

  • AC Current Monitor
    The hobby circuit below shows how a small current transformer from Magnetek can be used to monitor AC current to a load.  The AC voltage developed at the secondary of the transformer can be scaled so it can be read by any digital multimeter.  The transformer is rated at 30 amps.

 
  • DC CURRENT INDICATOR #4   December 15, 2008
    The circuit below uses some common components to turn on an LED whenever DC current above a certain level is detected.  The circuit uses a very popular LM393 dual voltage comparator from National Semiconductor and a common 1N4148 signal diode.  The diode acts as a crude 0.7v voltage reference.  Only one of the comparators inside the 8 pin package is used.  A pair of resistors across the diode forms a voltage divider, which produce a reference voltage of about 0.015v. ....
  • Electrical Current Indicator
    I designed this circuit as a simple current indicator for any load ranging from 40 watts to 250 watts.  The circuit turns on a small LED, whenever it detects current flowing to a remote load. 
    (added 12/04)
  • ISOLATED AC CURRENT MONITOR
    This circuit uses a small AC current transformer from Magnetek to produce an isolated voltage proportional to the AC current in the primary winding.  The transformer contains a single turn primary with a low 0.001-ohm resistance.  It can easily handle 30 amps of AC current and provides at least 500vac of isolation.  With the components shown, the output AC voltage is scaled so 1 amp of current produces 100mv of AC voltage.
  • Low Value Capacitance Meter
    This circuit was originally designed to measure the volume of fluid inside a medical syringe.   As designed, it produces a zero to 5 volt output, corresponding to a capacitance change of about 10 picofarads.  With a digital voltmeter, at its output, it can resolve a capacitance change of 0.002 picofarads or 2 femtofarads.
  • Pump Motor Monitor
    This circuit can turn on a light or sound a beeper, whenever an AC line powered pump motor turns on.  It is designed to detect the motor current using a small inductor placed on the outside of the motor’s power cable.  No direct wire contact is needed.


More Current Monitors / Sensors / Detectors Circuits

Master Category List - Dave's Circuits
 

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