Working with resistive sensor elements

Dear Control Engineering: I’ve read that RTDs (resistance temperature detector) are often the most precise temperature sensing devices. Given the relatively narrow range of resistance involved, how is it practical to get precision with two, three, or more decimal places on a Celsius scale?

02/27/2010


Dear Control Engineering: I’ve read that RTDs (resistance temperature detector) are often the most precise temperature sensing devices. Given the relatively narrow range of resistance involved, how is it practical to get precision with two, three, or more decimal places on a Celsius scale?

Sensors that measure a process variable using changes in resistance extend beyond RTDs. Thermistors also use resistance, as do many types of strain gages that are used in pressure and weight sensors. RTDs that use platinum wire can, at least in theory, measure temperature changes as small as 0.00001 °C. (Of course saying that one technology or another is the most accurate needs to be qualified in the context of specific types of application because few of those evaluations are true universally.) The kind of precision is only possible when coupled with highly sophisticated signal processing.

Modern electronics are capable of reading very small changes in resistance which makes this sort of thing possible. Interestingly enough, one of the basic elements of precise resistance measuring circuits dates back more than 150 years. The Wheatstone bridge is still the basic approach for quantifying very small changes in resistance that are characteristic of these sensing elements.

The traditional approach of four resistors arranged in a diamond formation is able to measure very small changes in resistance by looking at resistance differences. Explaining the physics of the process is a bit beyond this forum, particularly when others have done a much better job. Recently Dataforth published a six-page application note on the topic Basic Bridge Circuits. This goes well beyond basic high-school physics discussions and explains uses in industrial applications.

Download the application note.

–Peter Welander, process industries editor

Posted by Ask Control Engineering on February 27, 2010



No comments
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Motor specification guidelines; Understanding multivariable control; Improving a safety instrumented system; 2017 Engineers' Choice Award Winners
Selecting the best controller from several viewpoints; System integrator advice for the IIoT; TSN and real-time Ethernet; Questions to ask when selecting a VFD; Action items for an aging PLC/DCS
Robot advances in connectivity, collaboration, and programming; Advanced process control; Industrial wireless developments; Multiplatform system integration
Motion control advances and solutions can help with machine control, automated control on assembly lines, integration of robotics and automation, and machine safety.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Future of oil and gas projects; Reservoir models; The importance of SCADA to oil and gas
Big Data and bigger solutions; Tablet technologies; SCADA developments
SCADA at the junction, Managing risk through maintenance, Moving at the speed of data
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
click me