Smith Research & Technology, Inc.
Colorado Springs, Colo.

SRT has developed and manufactures a new line of inductive AC current sensor and AC voltage sensor. Our sensors utilize a patented design and manufacturing technique that often offers a better alternative to the use of toroidal current transformers (CT's) or hall effect devices. We use a gapped magnetic structure (herein referred to as a mag-gap), which permits a large number of turns and an attendant high voltage output. The mag-gap also eliminates saturation at higher currents and the dangerous conditions associated with open secondary windings of CT's. This new technology fills a void in today's AC sensor market and can help provide new solutions for today's complex automation designs. Our sensors can provide input intelligence for instrumentation or process/control applications. Without the need for auxiliary power to monitor current or voltage these sensors can provide convenience and flexibility for the design engineer.

Some SRT products deliver an AC voltage output of 3.5 Vrms (10 volt peak to peak), while other products have internal rectification to deliver a DC voltage output of 5.0 and 10.0 volts, or as a 4/20 mA driver. Most users employ programmable logic controllers (PLC's) or analog to digital converters to further process the output of our sensors, which is always a voltage proportional to the current or voltage being sensed.

Sometimes it is more desirable to activate another AC or DC control circuit at a known current or voltage rather than measure a value, so SRT has developed both a Current Actuated Switch and Voltage Actuated Switch. These units act as a normally open switch that is factory calibrated to close at a customer specified current or voltage. This in turn can activate another AC or DC device connected to that switch.

For energy management systems SRT has designed a microprocessor-controlled Smart Power Measuring Sensor (SPMS), which measure one voltage and one current while deriving operating power from the voltage being monitored. These sensors have isolated digital output and are typically polled by a host computer. Harmonic analysis performed within each sensor makes them appropriate for continuous monitoring of power quality. Their nonvolatile memory allows metering (including reactive power), and the ability to look back for the cause of an outage once power has been restored.

We manufacture two models of easy to install Clamp-on current sensors (U-Bar) for monitoring AC currents up to 1000 amps in cables over 2" in diameter. This type of sensor is ideal for attaching to large cables which are close to walls or are too big for our standard thru-hole sensors.

SRT also produces a DC product called the Battery Voltage Monitor which was originally developed for U.S. West Communications. It monitors DC batteries that range from 30 volts to 600 volts. This is our only DC powered device, obtaining its power from the batteries being monitored. The output of our battery monitor can come in either 5 VDC or 4-20 mA loop current.

Specifications in the form of .PDF files are available on a variety of 60Hz units (50Hz units are also available). Any specifications and/or response charts on the specific type sensor that you require can be performed at the factory and then faxed or e-mailed back to you.

Our sensors come in a variety of case sizes/thru-hole diameters, so there are Dimensional Drawings available on .pdf files, a Product Selection quick reference guide, and Photographs for your viewing . Price Guidance is also available, but exact pricing will depend on sensor used and any internal components necessary to meet your requirements. Please contact the factory for an exact price quote.

Here's more information on Using SRT Current Sensors, which can be of some help in selecting the proper sensor for your needs, and another page on the Most Desirable Characteristics for any inductive AC sensor.

Engineers at SRT are available to discuss any questions you might have regarding any of our products. Often we are asked to customize or prepare special calibrations on our sensors to suit customer needs. Please contact us at (800) 447-6805 and ask for Dayle Smith or Doug McNutt, or FAX us at (719) 634-2601, or send an E-mail to

Smith Research & Technology 3109 N. Cascade Ave., Bldg 201/202 Colo. Spgs., CO. 80907

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