A meter relay is a meter with a switched output that can be used to control a process or activate an alarm. In its simplest form, an analog meter relay uses mechanical contacts or a microswitch to operate an external device when the analog meter pointer reaches the level of the set pointer. Today’s analog meter relay has solid-state circuitry and a relay in place of a mechanical switch. (more…)
When Weschler started in 1941, panel meters were hand-made analog instruments. The typical meter had either a metal or bakelite case, a glass lens and an electro-mechanical movement. There were many US manufacturers during the 1940s and 1950s, including Triplett, Simpson, Weston, GE, Westinghouse, Beede, Hoyt, Hickok, Jewell, Marion, Supreme, and EMICO. Meters for DCV, DCA, ACV, ACA, and line frequency were standard.
This year Weschler Instruments celebrates its 80th year as a supplier of meters and instrumentation. Much has changed in electronic measurement equipment and technology since 1941. Vacuum tubes were replaced by transistors and then integrated circuits. Analog indicators became digital readouts and then graphical touchscreens. Manual operation migrated to automatic sequencing and then fully computerized tests. The basic electrical measurements are essentially unchanged: volts, amps, ohms, frequency, watts, etc. However, the range, precision, speed, safety, and ease of use have dramatically improved. Let’s take a brief look at some of the changes in three common field test instruments over the last 80 years. (more…)
The Weschler Temperature Measurement application note reviews the characteristics of popular sensors used to measure temperature: thermocouple, RTD (resistance temperature detector), thermistor, semiconductor, and infrared. This article surveys the instrumentation used in conjunction with these sensors for industrial temperature measurements. (more…)
Three devices are needed to make a 4-20 mA current loop – a transmitter, receiver and loop power supply. (more…)