Electroscope Circuit to Measure Electrostatic Charge

An electroscope is a tool that can sense and measure static electricity.

Static electricity happens when there is ,an imbalance of electric charges on something.

The electroscope can tell you if there is static electricity and how strong it is.

Just imagine the electroscope as a conductor.

When a charged object touches it, the electroscopes charges move around to react.

This movement creates an effect we can measure, which tells us about the original charge.

Circuit Working:

Parts List:

This do it yourself electroscope circuit is designed for precise measurement of electrostatic charge.

The charge to be assessed is stored on capacitor C1, which is a high quality MKT capacitor with a value of 1 to 2μF.

The voltage U across capacitor C1 is related to its charge Q through the equation U = Q / C1.

Operational amplifier IC2 functions as a buffer for this high impedance source.

An input lead is connected to one side of capacitor C1 and terminated with a test probe while the other side is linked to an earth lead and a convenient earth point.

IC2 amplifies the low voltage level at the output of IC1 and drives the moving coil meter M1 (±100 μA to ±1 mA center zero).

Switch S1 enables the selection between two measurement ranges.

When S1 is closed the amplification factor is 5, and when open the amplification factor is 10.

The internal impedance of M1 is 2.2k.

Alternatively, a digital multimeter can replace M1, and in such a case, resistor R4 2 to 20k can be omitted.

The operational amplifiers utilized in this circuit are MAX 4322 from Maxim.

These devices have a common mode input voltage that can reach the supply terminal and the outputs are capable of driving from rail to rail.

Formula:

Maxim Integrated created the low noise, precision operational amplifier known as the MAX 4322.

It may be applied to a variety of tasks that need for great precision and low noise levels.

Typically, the MAX 4322 is employed as a voltage follower or in other amplifier designs where low noise and accuracy are crucial.

You might set up the MAX 4322 in a high impedance buffer mode to connect with the sensitive parts of the electroscope so that it can sense electrostatic charge.

Here is a simple formula and some things to think about when measuring electrostatic charge in an electroscope circuit using the MAX 4322:

Voltage Gain Av:

It is possible to set up the MAX 4322 as a voltage follower (unity gain amplifier).

The voltage gain A_v in this setup is around 1.

Resistance at Input and Output:

The MAX 4322s extremely high input impedance typically hundreds of megaohms makes it useful for integrating with high impedance electrodes or sensors in the electroscope.

Because of the low output impedance, it is possible to drive measuring equipment or further stages without experiencing noticeable loading effects.

Voltage of the Power Supply:

Make that the MAX 4322 is receiving the proper power supply voltage (V_CC usually, about ±15V depending on the application).

Considering Noise:

Low noise characteristics of the MAX 4322 are crucial for sensitive measurement applications like as electroscopes, where tiny signals or electrostatic charges must be measured.

For the MAX 4322 used in a voltage follower configuration use the following formula:

• The output voltage V_out​ follows the input voltage V_in closely.
• The gain A_v​ is approximately 1.

Note:

Configuring the MAX 4322 as a high impedance buffer in an electroscope application allows it to precisely measure and magnify the electrostatic charge signals that the electroscopes sensor detects.

It is ideal for these kinds of exact measurement duties because of its high input impedance and low noise properties.

How to Build:

Building the DIY electroscope circuit involves assembling the components and connecting them according to the circuit diagram.

Prepare Components:

• Identify and gather all the required components.
• Ensure the values of resistors, capacitors and other components match the specifications in the circuit diagram.

Connect IC1 and Capacitor C1:

• Connect one side of capacitor C1 to an input lead which is terminated with a test probe.
• Connect the other side of capacitor C1 to an earth lead and to a convenient earth point.

Operational Amplifier IC1:

• Connect operational amplifier IC1 to buffer the high impedance source.
• Connect the output of IC1 to the input of IC2.

Digital Multimeter:

• If using M1, connect it to the circuit with its internal impedance of 2.2k.
• Alternatively, if using a digital multimeter omit resistor R4.

Switch S1 and Measurement Range:

• Connect switch S1 to enable the selection between two measurement ranges.
• When S1 is closed set the amplification factor to 5 and when open set it to 10.

Double check Connections:

• Double check all connections to ensure they match the circuit diagram.

Testing:

• Power on the circuit and test its functionality using a known electrostatic charge source.

Adjustments:

• Adjust digital multimeter to calibrate the electroscope for accurate measurements.

Fine-Tuning:

• Fine tune the circuit if necessary, and ensure the moving coil meter M1 provides the desired readings.

Finalize:

• Once the circuit is working correctly finalize the connections and secure the components in place.

Note:

• Remember to follow safety precautions double check component polarities and refer to the specific datasheets for the operational amplifiers and other components used in the circuit.

Conclusion:

This type of electroscope circuit is often used in physics and electronics experiments to demonstrate and measure the principles of electrostatics.

Keep in mind that specific circuit configurations may vary, and the detailed design depends on the intended application and desired features.

References:

An electronic electroscope

Electrostatic fieldmeter