B-Field Measurer

Description: This circuit generates an output voltage that is proportional to the magnetic induction (B) detected by its probe's coil. The coil must be sized to produce a full-scale, 10-V output corresponding to the maximum expected intensity of magnetic induction. The relationship between the magnetic induction (in tesla) and the output voltage (Vout) is defined by the equation A = number of turns multiplied by the average area of each turn, where R is the resistance of the coil and the probe, and C is the value of the capacitor. It is important that C is a low-leakage polypropylene or Teflon capacitor. In practical applications measuring magnetic fields in air, the coil will typically be small or very thin. For example, if R = 1 kOhm, C = 1 µF, and the coil consists of 100 turns with a mean area per turn of 1 cm², the circuit's output will be 1 mV/Gauss (1 T = 10^4 G). To operate the circuit, press the reset button and position the probe in an area free from magnetic fields, avoiding magnets and iron. Then, place the probe into the magnetic field to be measured and read the output voltage with a voltmeter. The intensity of the field can then be calculated using the appropriate equation. When building the instrument, it is essential to protect the op-amp's inputs from unwanted currents at the negative input. For full-scale outputs, a +15-V supply should be used for the op-amp.

This circuit is designed to effectively measure magnetic fields by utilizing a coil as a sensor element. The coil's design is critical; it should be configured to ensure that it generates the desired voltage output corresponding to the maximum expected magnetic field strength. The effective area of the coil, defined by the number of turns and the average area of each turn, plays a significant role in determining the sensitivity of the circuit.

The choice of capacitor is also important, as a low-leakage polypropylene or Teflon capacitor is recommended to minimize signal degradation over time. The circuit's output sensitivity can be calculated based on the parameters provided. For instance, with a resistance of 1 kOhm and a capacitance of 1 µF, the output voltage can be calibrated to provide a specific response to the magnetic field intensity, thus allowing for accurate measurements.

To ensure reliable readings, the circuit must be reset in a magnetic field-free environment. This step is crucial to eliminate any residual magnetic influence that may affect the measurement accuracy. Once the probe is placed in the magnetic field, the voltage output can be monitored using a voltmeter, allowing for straightforward calculations of the magnetic field intensity based on the output voltage.

When constructing the device, careful attention should be paid to the op-amp configuration, particularly regarding input protection. This will help prevent interference from unwanted currents, thereby enhancing the circuit's performance. The use of a +15-V supply for the op-amp ensures that it operates within its optimal range, facilitating accurate and stable output readings. Overall, this circuit serves as a practical tool for measuring magnetic fields in various applications, provided that the components are selected and configured with precision. This circuit develops an output voltage that is proportional to the magnetic induction, B, flowing through its probe"s coi l. You must size the coil to give a full-scale, 10-V output for your maximum expected magnetic-induction intensity. For a given value of (in tesla) and output voltage, Vout; where A is the effective area of your coil in m2 (A=number of turns average area of each turn), R is the resistance of the coil and the probe, and C is the value of the capacitor.

Notice that C should be a low-leakage polypropylene or Teflon device. For most practical applications that measure a magnetic field in the air, the coil will be either tiny or very thin. If R = 1 KOhmhm, C= 1 ¥, and the coil is 100 turns with a mean area per turn of 1 cm2, then the circuit"s output will be 1 mV/gauss (1 T= 104G).

To use the circuit, push the reset button and place the probe in an area that you know is devoid of magnetic fields. Be sure to avoid magnets and iron. Then, put the probe into the field to be measured and read the Vqut with a voltmeter. Finally, calculate the field"s intensity using the equation. When constructing the instrument, guard the op amp"s inputs from undesirable currents at the minus input.

For full-scale outputs, use a +15-V supply for the op amp.