Direct Testing of AC Path Using Multimeter Buzzer Range
A general digital multimeter cannot directly measure circuits such as capacitors, amplifiers, operational amplifiers, and AC circuits. But if the two ends of the piezoelectric ceramic chip of the digital multimeter are soldered with one foot, as shown in Figure 2, connected in series to a pair of socket A and B, and fixed to the battery box cover with the two holes exposed, many new functions can be added to the digital multimeter. Figure 2 Modification diagram of digital multimeter buzzer
1. Measure the communication pathway. DC cannot pass through the AC channel, so it is difficult to directly measure and determine whether the AC channel is damaged using a multimeter. However, using a modified multimeter for measurement is much simpler. Simply connect the A and B probes to the beginning and end of the AC channel. If the buzzer sounds, it indicates that the AC is unobstructed, otherwise it indicates that there is a circuit break in the circuit. To measure using the above methods, the "+" and "-" sockets of the multimeter must be short circuited, and the A and B sockets should be used for measurement. If you need to measure the DC path, you can insert the short circuit into the A and B sockets and measure it according to the general multimeter measurement method.
2. As a signal generator, it can be used to detect faults in multi-stage amplifier circuits. The method is as follows: (1) Connect the circuit under test to the power supply and put it in working state; (2) Connect either probe A or probe B to ground, and the other probe to the input terminal of the final stage of the amplification circuit; (3) Measure with an oscilloscope or speaker to see if there is a 1kHz output signal from the final stage. If there is an amplified signal output, it indicates that the fault is in the previous stage amplification circuit. Otherwise, it can be determined that the fault is in the current stage.
7, Using a digital multimeter as a thermometer
Many multimeters do not have temperature measurement settings, and it is necessary to record the temperature during each experimental class. Temperature control is required during PCB manufacturing, and using mercury thermometers can easily cause damage. The author can measure temperature by connecting a simple temperature measurement circuit externally. The measurement circuit includes a temperature voltage conversion circuit and a high-precision reference voltage source. The temperature voltage conversion circuit consists of integrated temperature sensors, integrated operational amplifiers, resistors, and other components. The high-precision reference voltage source consists of an integrated voltage regulator, capacitor, and resistor. The function is to compensate for the difference between 273.2K and 0 ℃ and achieve dimensional conversion. Adjust the voltage sensitivity of the measurement circuit to 1mv/℃. Then, place the digital multimeter conversion switch in the voltage range of 200mV and use the digital multimeter to directly display the measured temperature value.
