Simple ohmmeter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology
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More than ten years ago, the Radio magazine published a diagram of a very simple ohmmeter (see figure), which can measure the resistance of various parts in the range from several ohms to two megaohms. I have been using this device for several years now and am satisfied with its performance.
The main part of the ohmmeter, of course, is the dial indicator PA1. I used the M2003-M1 indicator with a 100 μA needle full deflection drain. Another indicator will do, but the measurement limits will be different. The indicator is connected to a measuring circuit composed of resistors R1, R2, battery GB1, switch SA1 and sockets X1-XXNUMX, to which the tested parts are connected.
When the switch contacts are open, parts such as resistors are connected to sockets X2 and X3. But first, these sockets are closed and the indicator needle is set with a variable resistor R1 to the final division of the scale - a conditional reference zero. After opening the sockets, a tested resistor can be connected to them. This is the first sub-range on which resistances can be read from approximately 0,9 kΩ to 2 MΩ. The greater the resistance, the less current flows through the indicator and the smaller the deviation of its arrow.
Having set the switch to the position of closed contacts, set the indicator arrow to zero, after which the resistor is connected to the sockets X1, X2 of the second subrange. Now the resistor under test will shunt the indicator, the arrow will deviate to a smaller angle with a lower resistance of the resistor. The measurement limits in this subrange are approximately from 9 ohms to 22 kOhm.
Author: A. Fedotkin, Maisky village, Perm region.
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