Ammeter selection

Choose an ammeter greater than 1/3 or 1/2 according to the rated current, mainly because the current will be too large when the load is cold started and it can display normally when there is an occasional slight overload. How to reasonably choose an ammeter, based on the accuracy requirements of the measured object, the accuracy of the ammeter, the inspection before measurement, the connection with the circuit under test, the correct reading, and the maintenance method of the ammeter.

1. Reasonable selection of ammeter

1) Reasonably select the accuracy of the ammeter based on the accuracy requirements of the measured object. Generally speaking, 0.1-0.2 level magnetoelectric ammeters are suitable for use in standard meters and precision measurements; 0.5-1.5 level magnetoelectric ammeters are suitable for laboratory measurements; 1.0-5.0 level magnetoelectric ammeters are suitable for It is used in industrial and mining enterprises for equipment operation monitoring and electrical equipment maintenance.

2) Select an ammeter with corresponding limit based on the magnitude of the current being connected. If the quantity limit is too large, the measurement accuracy will decrease; if the quantity limit is too small, the ammeter will be damaged. In order to make full use of the accuracy of the instrument, the measuring range of the instrument should be selected based on the principle of using the last 1/4 of the scale as much as possible.

3) Reasonably select the internal resistance of the ammeter. The smaller the internal resistance of the ammeter, the better.

2. Inspection of ammeter before measurement

Before measurement, check whether the ammeter pointer is aligned with the "0" scale line. If it is not aligned, adjust the "zero adjuster" to return the pointer to zero.

3. Connection between ammeter and circuit under test

1) When measuring, the ammeter should be connected in series to the low potential side of the circuit under test.

2) When measuring DC, you need to pay attention to the symbols of the ammeter terminals. For single-quantity limit ammeters, the measured current should flow into the ammeter from the terminal marked "+" and flow out of the ammeter from the terminal marked "-"; for multi-quantity ammeters, For the current limiting meter, the common terminal marked with "*" is the common terminal. If the other terminals are marked with the "+" symbol, the measured current should flow in from the "+" terminal and flow out from the "*" terminal; if the other terminals If the button is marked with a "-" symbol, the connection is exactly the opposite of the above situation.

4. Correct reading of ammeter

When reading, the pointer should be allowed to stabilize before reading, and try to keep the line of sight perpendicular to the dial. If the dial has a mirror, the pointer and the shadow of the pointer in the mirror should be kept overlapped to reduce the error.

5. Maintenance method of ammeter

1) Since the overload capacity of the magnetoelectric ammeter is very small, you must pay attention to the polarity and limit selection of the connecting circuit when using it.

2) If it is found during measurement that the pointer deflects in the opposite direction or in the forward direction beyond the full scale line on the scale, the power should be cut off immediately to stop the measurement, and the measurement can be performed again after the connection is correct or an ammeter with a larger limit is reselected.

3) When the measurement work is completed, the ammeter should be disconnected first, then removed from the measurement circuit, and placed in a dry, ventilated and cool environment. For microammeters and milliammeters with high sensitivity and accuracy, wires should be used to connect the positive and negative terminals to protect the measuring mechanism of the meter.