القياسات في الدارات الالكترونية .. الإلكترونيات

Measurements in electronic circuits .. Electronics

Measurements in electronic circuits

Multiple measurements determine the operating conditions in electronic circuits, the simplest of which are those that are carried out in stable operating conditions in terms of voltage or current. The moving coil meter consists of a permanent magnet that gives a strong magnetic field and a coil in which the current passes through a fine spiral wire (250). In addition, the current controls the rotation of the coil and gives a complete deflection when its value is 6 milliamps, where the indicator moves to the end of the existing gradient. It is known that the current passing through the resistor is equal to the voltage divided by the resistance. Therefore, the resistors in series with the device are useful in determining the value of the existing voltage.

As for Figure (251), it includes resistors M1, M2, M3, which are useful in measuring the following voltages: 2.5 volts, 10 volts, 100 volts, and a current scale with a value of 0.25 amperes. Therefore, the value of these resistors is: M1 = 10,000 ohms, M2 = 40,000 ohms, M3 = 400,000 ohms. However, if we want to use the device to measure high-intensity currents, it must be connected in parallel with a specific resistance. If we assume that 10/9 of the current value passes through this resistance, then only 1/10 of the total current remains to pass through the device itself (252). The multimeter (253) is characterized by having a switch that allows it to give nine different positions.

250 - The measuring device with a moving coil is the basis for the operation of most devices.

251 - Increasing the range of voltage measurement.

252 - Resistors in parallel.

253 - Multimeter circuit.

In position 1, the resistor M1 is connected to the device in series to measure the voltage. Positions 2, 3, 4 and 5 allow measuring other voltage values ​​and in them M2, M3 and M4 are connected in series with the resistor so that the higher the voltage value, the more resistors are required. Positions 6, 7, 8 and 9 allow the device to be used to measure high intensity currents in which the resistor is permanently connected in parallel with the device. If we assume that the total deflection of the device gives 0.5 amperes without a parallel resistor, or 1 ampere with a parallel resistor, this results in: M1 = 2.5 kΩ for a voltage of 2.5 volts, M2 = 10 kΩ for a voltage of 10 volts, M3 = 90 kΩ for a voltage of 100 volts (10 kΩ is already present), M4 = 150 kΩ for a voltage of 250 volts.