The current loop is a widely used industrial control circuit topology. The basic current loop has three elements:
A DC current shunt is a specialized resistor used to measure high currents. The shunt is wired in series with a heavy load, such as a DC motor, battery charger, heater, plating bath or smelter pot line. A DC voltmeter is connected to the shunt in a 4-wire (Kelvin) configuration. The shunt has bolt holes or
There are two common methods for performing insulation tests on cables, wiring and electrical equipment. One uses a megohmmeter to measure insulation resistance. The other uses a hipot tester to check for insulation breakdown. Both apply a high voltage, either ac or dc, to the device under test (DUT) and measure the resulting current flow. (more…)
Alternating current (ac) measurements involve more factors than direct current (dc) measurements. Let’s look at how some of these affect the measurement. We’ll focus on signals with a fundamental frequency below 1kHz. This is where digital multimeters and panel meters are typically used. Higher fundamental frequencies require instrumentation with wider bandwidth, such as audio meters or oscilloscopes. (more…)
The National Electric Code (NFPA 70) defines a switchboard as ‘a large single panel, frame or assembly of panels on which are mounted… switches, overcurrent and other protective devices, buses, and instruments.’ A hundred years ago, the typical switchboard had knife switches, fuses, analog meters and other electrical apparatus mounted on a slate panel. It was large, heavy and live front, meaning hazardous voltages were exposed to the operator. (more…)