In this article we discuss a simple high voltage meter circuit which can be used for measuring extremely high voltages in the order of many 1000s of volts.
The circuit can be used to measure high voltages from
- CDI units,
- Automobile spark plugs,
- high voltage generators,
- mosquito bat circuits,
- fence chargers,
- room ionizer circuits etc.
The voltage detecting IC CA3140 is a MOSFET input op-amp with the ability to measure voltages below the negative supply rail, which eliminates the need for dual supplies. A single IC allows us to construct a circuit which can measure up to 10,000 volts without adversely effecting the circuit, thanks to the extraordinarily high input resistance of 1000 Meg Ohms (R1 to R10) attached to the probes of the FET op-amp.
The voltage across R11 is reduced to a acceptable level through resistors R1 to R10 (100 Meg each). This stepped down voltage is detected by IC1 and supplied at its output to the current meter for displaying the high voltage. IC1 is wired as a voltage follower, which means it outputs the same voltage which is detected across R11 (its input). As a result, it serves as an impedance converter, supplying power to the 100uA meter.
This meter is connected via a series resistor which can be appropriately adjusted to convert the ammeter into a voltage meter that reads in kilovolts.
The calibration procedure is quite easy. Start by adjusting the meter to zero using the RV1 preset. This is done by keeping the probe tips shorted and by keeping the meter on the 5kV range through the SW1 switch.
Next, switch the meter on the 10kV range through the SW1 and simply put a 1V DC supply across R11.
After this, adjust PR1 until the meter needle reaches to a full scale reading of 10kV.
Now, adjust SW1 back on the 5kV range and connect a 0.5 V DC across R11 and adjust PR2 until a full scale deflection is achieved on the meter corresponding to a 5 kV on the scale. The meter dial can be graduated with calibrations of 0-10kV in 1 kV steps on the upper side of the meter, and create markings of 0-5kV in 1kV steps on the lower side, just below the 10kv graduations.
The power supply DC for this high voltage meter circuit can be derived from any ordinary 9V PP3 battery, or a regulated 9V DC from a AC to DC adapter.