Three devices are needed to make a 4-20 mA current loop – a transmitter, receiver and loop power supply. (more...)
Category: Blog
Basic 4-20 mA Current Loops
The current loop is a widely used industrial control circuit topology. The basic current loop has three elements:
- A transmitter that sends a dc current around the loop
- A receiver that measures the current in the loop
- DC voltage supply that powers the loop (more...)
Using DC Current Shunts
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. (more...)
AC Measurement Considerations
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, (more...)
What is a Switchboard Meter?
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. (more...)