Ignore the Interfering Factors of the Measurement Environment on the Clamp Ammeter
Whether it is a transformer-type clamp ammeter or an electromagnetic system clamp ammeter, the measurement principle is based on the effect of the electromagnetic field generated by the current in the measured conductor. Since the electromagnetic field can play a role in the measurement work of the clamp ammeter, then other substances that can generate electromagnetic fields, or can conduct magnetic and electrical conduction must also play a role, but it is just a side effect - interference. There are many kinds of interference sources that can produce interference, such as motors, transformers, electromagnets, current-carrying conductors, permanent magnets, and larger ferromagnetic substances. Therefore, when measuring, the clamp ammeter (especially the electromagnetic clamp ammeter) must avoid the source of interference and keep a distance from it as much as possible. For example, when measuring the running current of the motor, the clamp ammeter should be as far away from the motor as possible. The meter cannot be pasted on the motor casing, and the measurement error caused by this may be very large.
Blindly choose the range or directly measure regardless of the range
Clamp-on ammeters have poor overload capacity, and it is not possible to use small-range gears to measure large currents, otherwise, it is easy to cause damage to the measurement circuit or the meter head. Therefore, the range must be selected reasonably, and the pointer should be expected to be in the middle of the scale according to the range of the measured current. If the current to be measured cannot be estimated in advance, it is advisable to select the maximum limit for testing first, and then switch to an appropriate range according to the measurement results.
Ignores the number of wires under test clamped in
According to the design principle of the clamp ammeter, when it is desired to measure the current flowing through a certain conductor, the clamp ammeter can only be clamped into the conductor, and other current-carrying conductors that do not participate in the measurement must not be clamped in at the same time. For example, when measuring the operating current of each phase of a three-phase power circuit, it must be measured one by one, and it must not be clamped into two-phase or three-phase lines at one time. For the working neutral line (N line), there is also current flowing under normal circumstances. , the existence of the current and the phase problem of the current cannot be ignored. Even power lines such as secondary control lines and instruments cannot be ignored when the measured current is small.
Ignore the clamp-in position of the wire under test
The clamp probe (iron core jaw) of most clamp ammeters adopts an approximately rectangular structure. To obtain accurate measurement results within the reach of the clamp ammeter, it is required that the current in the conductor under test be within the clamp The magnetic induction intensity generated in the probe core is relatively uniform in all parts. At this time, the best position for the measured wire to be clamped should be at the geometric center perpendicular to the jaw plane. If the position of the measured wire deviates from the optimal position, the measurement error will increase significantly, and may exceed 5% at the maximum.
Ignoring the engagement of the jaws
The clamp probe of the clamp ammeter is mostly made of metal magnetic materials such as silicon steel sheet and permalloy. When the moving iron core of the jaws of the clamp probe is closed with the static iron core, the two contacting end surfaces should be closely matched. If the joint state is not good, it is often accompanied by "squeak" electromagnetic noise. Hold the palm of the handle of the clamp ammeter At this time, you will feel the collision vibration between the contact surfaces of the jaws. If the jaws are poorly joined, it will inevitably affect the accuracy and linearity of the measurement, and sometimes even fail to measure. Therefore, attention should be paid to the joint status of the jaws. When poor joints occur, the jaws should be re-opened and closed once to several times. If the fault still cannot be eliminated, check whether the end faces of the jaws are damaged, whether there is dirt, rust or not. For foreign matter such as traces, measures such as wiping, cleaning, and grinding can be taken to restore a good joint state.
