The heating tube has simple structure, high thermal efficiency, good mechanical strength, and good adaptability to harsh environments. How to judge whether the heating tube is good or bad? You can use a multimeter to measure two aspects:
1, the resistance of the two outlet wires should be normal, 220V, 1000W about 48 ohms, 1500W about 32 ohms, and so on.
2, the resistance between any one of the outlet wires and the shell is more than a few megohms. Those who can pass the above two steps are good. A multimeter is a relatively precise instrument. If used improperly, it will cause inaccurate measurement and extremely easy damage. However, as long as we master the use and precautions of the multimeter, and proceed with caution, the multimeter can be durable.
The following items should be paid attention to when using a multimeter:
1. When measuring DC voltage and DC current, pay attention to the polarity of "+" and "-", and don't connect them wrongly. If you find that the pointer is turned on and off, you should immediately replace the meter rod to avoid damage to the pointer and meter head.
Heating pipe
2. When the multimeter is not in use, do not rotate it in the resistance position, because there is a battery inside. If you are not careful, it is easy to short-circuit the two meter rods, which will not only consume the battery, but even damage the meter head in serious cases.
3. When measuring the resistance, do not touch the naked ends of the component with your hands, so as to avoid the parallel connection of the human body resistance with the measured resistance, which will make the measurement result inaccurate.
4. The measuring current and voltage cannot be rotated in the wrong gear. If the resistance gear or current gear is mistakenly used to measure the voltage, it is very easy to burn the meter. When the multimeter is not in use, it is best to turn the gear to the highest AC voltage to avoid damage due to improper use.
5. If you do not know the magnitude of the voltage or current to be measured, you should first use the highest gear, and then select the appropriate gear to test, so as to avoid excessive deflection of the needle and damage the meter head. The closer the selected gear is to the measured value, the more accurate the measured value will be.
6. When measuring resistance, if the two meter rods are short-circuited and the "zero ohm" knob is adjusted to the maximum, the pointer still does not reach 0 point. This phenomenon is usually caused by insufficient battery voltage in the meter, and it should be replaced with a new one. The battery can only be accurately measured.