An electroscope is a tool used to measure and identify static electricity.
Static electricity is caused by an imbalance of electric charges on an object.
Static electricity levels and presence are both measured through the electroscope.
Just think of the electroscope as a conductor.
When a object is charged it comes into contact with the electroscope where it charges fluctuate and react to it.
This movement produces an effect that can be measured and provides information about the original charge.
Circuit Working:
Parts List:
| Category | Description | Quantity |
|---|---|---|
| Resistors | ||
| 100k 1/4 watt | 2 | |
| 10k 1/4 watt | 1 | |
| R4 (2 to 20k range) | 1 | |
| Capacitors | ||
| Ceramic C1 (1 to 2μF range) | 1 | |
| Electrolytic 1μF 16V | 1 | |
| Semiconductors | ||
| IC MAX 4322 | 2 | |
| ON/OFF Switch | 1 | |
| Meter 100uA center 0 | 1 |
The purpose of this DIY electroscope circuit is to detect electrostatic charge correctly.
Capacitor C1 an excellent MKT capacitor with a value of 1 to 2μF stores the charge that has to be measured.
The formula U = Q / C1 provides a relationship between the voltage U across capacitor C1 and its charge Q.
This high impedance source is protected by the operational amplifier IC2.
One side of capacitor C1 has an input lead connected to it which is terminated with a test probe.
The other side is connected to a ground lead and serves as a ground point.
IC2 powers the moving coil meter M1 (±100 μA to ±1 mA center zero) by boosting the low voltage level at IC1s output.
There are two measurement limits to choose from due to Switch S1.
The amplification factor for S1 is 5 and when it is closed it is open to 10.
M1 has an internal impedance of 2.2k.
Also resistor R4 2 to 20k could be avoided if a digital multimeter is used in place of M1.
The Maxim MAX 4322 operational amplifiers are used in this design.
These devices can drive from one rail to another and their outputs can reach the supply terminal with a common mode input voltage.
Formula:
The MAX 4322 is a low noise quality operational amplifier designed by Maxim Integrated.
It is often used for a number of activities requiring high accuracy and low noise levels.
The MAX 4322 is usually found in amplifier designs where accuracy and low noise are essential such as as a voltage follower.
To enable the MAX 4322 to detect electrostatic charge one must arrange it in a high impedance buffer mode to connect to the electroscopes sensitive components.
When using the MAX 4322 to measure electrostatic charge in an electroscope circuit keep the following simple formula in mind:
Av Voltage Gain:
The MAX 4322 can also be configured as a unity gain amplifier or voltage follower.
In this configuration the voltage gain Av is around 1.
Input and output resistance:
The MAX 4322 is helpful for integrating with high impedance electrodes or sensors in the electroscope because of its extremely high input impedance which is generally hundreds of megaohms.
The low output impedance makes it easy to run extra stages or devices for measurement without seeing any loading effects.
The power supplies voltage:
Check that the MAX 4322 is getting the right voltage from the power source (VCC often about ±15V depending on the application).
Taking noise into the account:
For easy measurement applications such as electroscopes where it is necessary to measure minute signals or electrostatic charges the MAX 4322s low noise characteristics are necessary.
Use the following formula when using the MAX 4322 in a voltage follower configuration:
- The input voltage Vin is closely followed by the output voltage Vout.
- Av the gain is around 1.
Take note:
The MAX 4322 is capable of tracking and increase the electrostatic charge signals that the electroscopes sensor detects when it functions as a high impedance buffer.
Its high input impedance and low noise qualities make it perfect for these kind of accurate measuring tasks.
How to Build:
To build a Electroscope Circuit to Measure Electrostatic Charge following steps are required to follow:
Prepare Components:
- Check and gather all the required necessary components as mentioned in the above circuit diagram.
- Be sure the values of resistors, capacitors and other components match the specifications in the circuit diagram.
Connect IC1 and Capacitor C1:
- Connect capacitor C1s one side to an input terminal that has a test probe connected to it.
- Connect the other side of capacitor C1 to an ground lead and to a convenient ground 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 meter connect it to the circuit with its internal impedance of 2.2k.
- Remember if using a digital multimeter omit resistor R4.
Switch S1 with Range of Measurements:
- When choosing between two measurement ranges connect switch S1.
- Set the amplification factor to 5 when S1 is closed and to 10 when it is open.
Verify connections again:
- Verify all connections one more time to make sure they match up with the circuit schematic.
- Turn the circuit on then use an approved electrostatic charge source to test its operation.
Modifications:
- To get exact measurements tune the electroscope using a digital multimeter.
Adjusting:
- If required adjust the circuit and make sure the moving coil meter M1 gives the right values.
Complete the circuit:
- Place the components in proper spot and complete the connections after the circuit is operating well.
Conclusion:
The Electroscope Circuit to Measure Electrostatic Charge are often explained and measured in physics and electronics studies using this kind of electroscope circuit.
Note that particular circuit designs might differ and how they are used and desired features decide the particular design.