Setra Blog

Converting mA to voltage is common in HVAC when working with pressure transducers. Terminology to keep in mind includes:

• 1 mA = 0.001 AMP (short for amperes)
• Amps are referred to as CURRENT
• Resistor values are in OHMS (Ω is the symbol for ohms)
• VOLTAGE is the result of passing amps through a resistor

Pressure transducers today are more rugged and reliable than ever. Made of stainless steel construction, they provide abundant overpressure protection, improved total error band, and offer negligible orientation and vibration effects. They are ideal for long-term use even in harsh environments of extreme temperature, humidity, and vibration.

The accuracy of differential pressure transducers has greatly improved to provide better solutions for demanding applications. This article discusses why accuracy is an important consideration when selecting a pressure transducer for low-differential, critical pressure applications.

Total Error Band (TEB) is a measurement of worst case error; it is the most comprehensive and concise measurement of a sensors true accuracy over a compensated temperature range.  TEB is extremely important to know when trying to determine how well a sensor will work within a particular design system. By calculating TEB you'll be able to understand the different possibilities for error. Formulating TEB can be tricky if you don't have the right inputs readily available. 

Any design engineer must seriously consider the manufacturing environment when looking to select a pressure transducer for inclusion within a refrigeration chiller, pump, engine test equipment, or other machinery. The life of a pressure transducer is proportional to the system design and assembly process. 

Which method provides better accuracy?  Non-linearity as the End Point Method is the relationship of the calibration curve to a specified straight line through its endpoints (i.e. Zero and Full Scale). Best Fit Straight Line (BFSL) method is the relationship of the calibration curve to a calculated straight line that minimizes the error but does not pass through the end points. BFSL method effectively cuts the end point value in half.

Many of the following technical specifications appear on datasheets for pressure transducers and similar devices. Here we review their technical definitions and relationships.

Root Sum Squares (RSS): accuracy of a pressure transducer is calculated by taking the square root of non-linearity + hysteresis + non-repeatability.

Shock & vibration are two potential mechanical problems for pressure transducers.

Shock is a sudden, unexpected impact that transmits energy to a device in a relatively short time interval. For a pressure transducer, that energy passes through the stainless steel up through the housing. Shock may originate from rough transportation and handling, such as by trucks, forklifts and conveyors. Alternately, shock can be caused simply by dropping the transducer on the shop floor or by an assembler slamming a cabinet door adjacent to it. A transducer may not be damaged by a single shock, but can experience fatigue failure with numerous low-level shocks over the course of its life.

Capacitance based pressure transducers provide many benefits over other technologies. 8 features that should be considered when choosing a pressure transducer are accuracy, minimal mechanical motion, range capabilities, long term stability, high-level output, media compatibility, electromagnetic compatibility and resistant to harsh environments..

Often we hear terms used to describe pressure transducers or terms commonly used in the HVAC/R and industrial industries, but there may be some confusion as to their meaning. Here are a few commonly used terms and their definitions.