- 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.
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- 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. ....
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- 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)
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- 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.
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- 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.
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- 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.
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