Refinement of the ammeter of alternating current. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Refinement of the ammeter of alternating current. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Measuring technology

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Electromagnetic ammeters E8025, E8030, E8031 are usually designed to measure alternating current of several tens of amperes. They are unpretentious in operation, durable, do not require maintenance, do not need a power source. For normal home use, such meters are ineffective, since household electrical appliances rarely, individually or even in total, consume more than 10 ... 15 A. However, if you often need to measure alternating current in a 50 Hz network of lesser strength, then such ammeters can easily be made more sensitive.

The E8030 ammeter, originally designed to measure alternating current 20 ... 50 A, has undergone refinement.

To do this, the ammeter is disassembled and the frame with the coil is removed from the metal base. The latter is wound with multilayer copper tape and consists of three turns. Instead, a new winding is wound, which should contain 37 turns of a bundle of ten pieces of PEV-2 0,27 wire twisted together or another similar one (Fig. 1). With such a coil, the ammeter will measure an alternating current of 2 ... 5 A (this value was chosen so as not to make a new scale, but it may be different). When installing the coil on the metal frame of the device, do not forget to install the oval metal adjustment lever (fig. 2, bottom right).

Refinement of the AC ammeter
Rice. 1. New coil winding

Refinement of the AC ammeter
Rice. 2. Oval metal adjustment lever

To calibrate the device, it is convenient to use a step-down transformer with an overall power of 90 VA and a secondary winding of 12 V. A series circuit is connected to it, composed of a calibrated device, an exemplary AC ammeter and a load, which can be used as incandescent lamps, powerful fixed resistors or rheostat. For the ammeter being converted, the middle of the scale corresponds to a value of about 3 A. Having set such a current in the circuit, move the adjusting lever to the middle position and, unwinding the turns from the coil one by one, bring the ammeter needle to the scale mark of 3 A. Having achieved this and increasing the current in the circuit to 5 A , by moving the adjusting lever, set the arrow to the corresponding mark on the scale. Both adjustments are partially interdependent, so they will have to be repeated several times. Use a non-magnetic tool to move the adjusting lever.

After completing the calibration, the coil leads are shortened as much as possible and soldered to the contact screws. The finished coil must be impregnated with varnish XB-784 or similar. The view of the ammeter assembly is shown in fig. 3.

Refinement of the AC ammeter
Rice. 3. View of the ammeter assembly

It is convenient to use such meters to control the operation of various equipment in a home workshop, garage. For example, you can track overload in the work of metal and woodworking machines in time.

To convert ammeters to a higher current, the number of turns of the coil is proportionally reduced, and the total cross section of the winding wire is increased. The AC voltage drop across the ammeter when it is converted to a limit of 5 A should be no more than 0,3 V, i.e., the power dissipated by the measuring coil should not exceed 1,5 W. Otherwise, the coil should be rewound with a wire with a large copper cross section. When operating such and similar ammeters, it should be borne in mind that they are a source of acoustic noise, it is quiet, but at night it can be noticeable in a residential area.

Author: A. Butov

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