you need
  • - Ammeter;
  • - Tester;
  • - known conductor cross-section of a known material;
  • - resistivity table.
Connect ammeter shunt in parallel to expand the possibilities of its measurement.In this case, the main passes through the shunt current, and that part of it which is to be measured passes through the ammeter.Rated current network calculated according to a special formula.
To calculate the shunt, find the maximum current that the device will have to be measured.To do this, measure the voltage on the power source of U in volts and divide it by the total resistance of the chain R in ohms.All measurements are made tester if the current constant at the same time take into account the polarity
of the device.Search rated current of the circuit, the voltage dividing resistance I = U / R.Look at the scale of the ammeter to find the maximum current that it can be measured.
Find a shunt resistance.To do this, measure the intrinsic resistance ammeter R1 in ohms, and find the right shunt resistance by dividing the product of the maximum current that can be measured by the instrument I1 and its resistor R1 to the rated current of the network I (R = (I1 ∙ R1) / I).
example.It is necessary to measure the current in a circuit where the maximum value of up to 20 A. For it is proposed to use an ammeter to measure the maximum possible current of 100 mA, and 200 ohms.Shunt resistance in this case is R = (0,1 ∙ 200) / 20 = 1 ohm.
as shunts, use standard resistors.If those are not available, the shunt fabricate themselves.To produce grafts take best conductors of copper or other highly conductive material.To calculate the required length of the shunt conductor l, take the famous wire section S and find the resistivity of the material ρ, which is made from this device.Then, the resistance R, multiply by-section, measured in mm², and divide by its resistivity, expressed as ohm ∙ mm² / m, taken from a special table l = R ∙ S / ρ.
In order to make a shunt for an ammeter from the above example of copper wire cross section 0.2 mm², take its length, which is calculated by the formula l = 1 ∙ 0,2 / 0,0175 = 1143 m. The same principle is used when bypass any other part of the circuit.