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The transformer ratio arm bridge or TRA bridge is a type of bridge circuit for measuring electronic components, using a.c. It can be designed to work in terms of either impedance or admittance . It can be used on resistors, capacitors and inductors, measuring minor as well as major terms, e.g. series resistance in capacitors.
The effective series resistance of the primary winding is set by the burden resistor on the secondary winding and the transformer turns ratio , where: = /. The core of some current transformers is split and hinged; it is opened and clipped around the wire to be sensed, then closed, making it unnecessary to free one end of the conductor and ...
An ideal transformer is a reasonable approximation for a typical commercial transformer, with voltage ratio and winding turns ratio both being inversely proportional to the corresponding current ratio. The load impedance referred to the primary circuit is equal to the turns ratio squared times the secondary circuit load impedance. [7]
Many digital clamp meters utilize a current transformer for measuring alternating current (AC). Current transformers are used extensively for measuring current and monitoring the operation of the power grid. Along with voltage leads, revenue-grade CTs drive the electrical utility's watt-hour meter on many larger commercial and industrial supplies.
To match the impedances, both cables must be connected to a matching transformer with a turns ratio of 2:1. In this example, the 300-ohm line is connected to the transformer side with more turns; the 75-ohm cable is connected to the transformer side with fewer turns. The formula for calculating the transformer turns ratio for this example is:
In a ratio meter, therefore, it follows that the force produced by one coil will always tend to rotate the measuring element in the opposite direction to the force produced by the second coil, and further more, as the magnetic field is of non-uniform strength, the coil carrying the greater current will always move towards the area of weaker ...