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…)
Selecting a panel meter for a particular application can be a daunting task, given the wide variety of products that are available today. There are many factors to consider when making a decision. Let’s look at a few of the major items.
Specifications for panel meters and test instrumentation usually include an accuracy value. This number defines the maximum amount the meter reading or transmitter output will differ from the ideal value, as determined by an established reference standard. Accuracy is usually expressed as either a percent of reading or a percent of range. (more…)
Process calibrators are handheld, battery-powered instruments used for field testing and calibration of industrial process equipment. The typical calibrator has a one or two-parameter digital display, function switch and up/down buttons for output level adjustment. Some models have a dial knob for level adjustment, which many users say is quicker to adjust. Common types of process calibrators are voltage, loop, temperature, and multi-function. (more…)