Calculate the resistance value of the heating tube according to the parameters, and then measure it with the appropriate resistance file of the multimeter according to the resistance value. In fact, the resistance generally has a cold state and a hot state, and the multiple of the difference is 10 times larger depending on the material. Therefore, the test is not a constant standard, as long as it is not 0 (short-circuit the test lead first, look at the displayed data, and measure the resistance value of the heating tube to subtract the data when the short-circuit is connected), or the resistance value is greater than 100 ohms. It shows that the heating tube is good, otherwise there will be problems.
Digital multimeter
Of course, you can use a multimeter to measure AC and DC (multimeters are divided into digital multimeters and pointer multimeters):
Digital multimeter to measure AC voltage: connect the black test lead to the ground (marked in the test lead socket), and the red lead to the AC (or V letter plus one) hole; the gear refers to 750 in the AC~ column (some is 1000) ( If it is to measure the mains 220V) range. Then the two pens touch the two holes of the power socket respectively, and the reading is the AC voltage value.
Digital multimeter to measure DC voltage: the same measurement AC, only the red pen is connected to + hole, the red pen is also in contact with the power supply + pole, the gear is in DC (or a dash under the V letter) gear, the range depends on the specific situation, from Big to small. For example, when testing a AA battery, select the 2V range. If the polarity is reversed, there will be a negative display before the reading.
Pointer meter to measure AC voltage: connect the black pen to negative or ground, the red pen to +, the gear is set to AC~500V, insert two pens into the digital multimeter, and the number pointed to by the pointer should be read corresponding to the maximum range on the right: optional If it is 500V, the reading should look at the row with the largest number marked 50 on the right side of the reading plate. If the pointer points to 20, then the reading is 200V.
Pointer multimeter to measure DC voltage: same as the measurement method of digital multimeter, the reading is the same as the above measurement of AC voltage; when the positive and negative poles of the DC voltage cannot be determined, it can be measured as AC first, but the reading is not concerned, just reverse the polarity of the test pen In the performance test, see which of the two measurements the pointer is deflected, then the positive and negative polarity that the test pen touched this time is the correct positive and negative polarity. Then set the gear to the appropriate range of the DC voltage and measure the reading.
The difference between AC voltage and DC voltage
AC voltage is a voltage whose direction and size change periodically; DC voltage is a voltage whose direction and size remain constant.
Notice:
1. The AC voltage changes periodically rather than randomly;
2. Direct current is based on voltage rather than current.