Increase the anti-interference performance of the digital multimeter
Digital multimeters are widely used and have the advantages of high input impedance and intuitive readings. However, in some applications, the clutter scattering of motors or devices will interfere with the digital multimeter. Anti-interference function. In fact, the anti-measurement interference measures of general digital multimeters are not complicated in principle. Usually, a low-pass filter circuit is connected in series in the measurement circuit to suppress conducted interference. The simplest measure to suppress high-frequency interference is to connect a coil in series in the measurement circuit, and the coil should be as close as possible to the input port of the multimeter. The coil can be considered to use a wire-wound coil with a magnetic core. Compared with an air-core coil, it has the characteristics of large inductance and less deformation under pressure. Cut off the meter stick, close to the input terminal of the multimeter, connect the inductance device in series, and finally seal it with a heat-shrinkable sleeve on the outside, which is very beautiful and durable. If the user is reluctant to cut off the connection of the meter stick, you can also try to clamp the magnetic ring on the side of the connection line close to the multimeter, and wind it a few more times, which also has the same effect as the inductance in series. It should be noted that after the low-pass filter is connected in series in the measurement circuit of the multimeter, it will affect the measurement of high-frequency AC signals (related to the characteristics of the low-pass filter), so in conventional measurements, the characteristics of the low-pass filter related), so in routine measurement, if the multimeter is not significantly disturbed, there is no need to add a low-pass filter.
Advanced Multimeter Fuses
The built-in fuse (commonly called "fuse") of advanced multimeters is expensive, and the price of an original accessory fuse for FLUKE high-end watches is almost equivalent to a domestic entry-level multimeter. Buying such fuses from different channels has a huge price difference, and the quotations you get at the fuse device counter and the instrument counter in the electronic market will vary greatly. For fuses, as long as the size is the same, the fusing current and breaking voltage parameters are the same, and the fusing speed characteristics are equivalent, they can be completely substituted. In addition to looking at the fusing current, the choice of a fuse should also pay attention to the high-voltage breaking capacity. This is the difference between some fuses marked 250V/1A and 000V/1A.
The breaking capacity refers to whether the fuse can effectively block the conduction of current after the fuse is blown under the extreme high voltage state, because in extreme cases, the high voltage will generate an arc in the air to continue to conduct the current. Although the breaking capacity of fuses is often overlooked by non-professional users, it is related to operational safety and should not be underestimated. Users who use low breaking rating fuses as substitutes should not use it to measure high voltage. In fact, many electronics hobbyists only work with low voltages when they complete small electronics projects. Conventional fuses will not blow immediately within tens of seconds when the current reaches the rated current or even exceeds one point, and have delay characteristics, so high-end multimeters will choose fast-acting fuses that blow immediately to protect sensitive and expensive electronics. equipment. FLUKE mainstream and high-end watches commonly use two fuses of 440mA and 11A. Famous fuse brands in the industry include Bussmann and Litelfuse. SIBA is also the preferred fuse brand for many advanced instruments and is a good substitute. It should be noted that some cheap big-name or so-called original fuses on the Internet are imitation products, which have large fusing current errors and slow response speeds, which cannot protect advanced instruments well.
