Pressure Transducers & Pressure Transmitters: Pressure Transducers & Pressure Transmitters

Introduction to Pressure Transducers & Transmitters
What is a pressure transducer? A pressure transducer is a transducer that converts pressure into an analog electrical signal. A transducer produces millivolts, amplified voltage, or current output; however, a transmitter produces current output only. Pressure transducers and transmitters convert an applied pressure into an electrical signal. This signal is both linear and proportional to the applied pressure. Pressure sensors, transducers, and transmitters are commonly referred to as just pressure transducers. The output electrical signal is sent to computers, PLC's, chart recorders, digital panel meters, or other devices that interpret this signal and use it to display, record, and/or change the pressure in the system being monitored. The most popular output signal is a 4-20 mA current output. Other voltage signals such as 0-5/10 VDC are also used in some applications. All transducers require an input (also referred to as excitation or supply voltage) in order to power the internal circuitry. FTB transducers use FTB-patented and developed sensing/sensory system to accurately measure the pressure from the application. Other than those pressure sensors (strain gauge, piezoresistive and thin film) available on market for most of the use on pressure transducers, FTB pressure transducers are unique and capable of being used in both low and high pressure applications up to 15,000 PSI.

Pressure Transducer Types
General Purpose Transducers provide excellent performance, reliability and value for a wide variety of electronic pressure measurement applications. General purpose transducers are available with a 4-20mA or 0-10VDC output.
Industrial Grade Transducers are precision engineered to fit the majority of industrial pressure measurement applications. Each unit undergoes quality control testing and calibration to achieve a higher accuracy. The printed circuit board uses state of the art surface mount technology and is potted in silicone gel for protection against vibration, shock, and humidity. Industrial models have a 4-20mA output signal and offer pressure ranges including vacuum, and pressures up to 5000 PSIG. Advantages of the industrial grade model include higher accuracy, zero & span adjustment for recalibration, and better resistance to vibration, shock and humidity than most transducers on the market. However, FTB pressure transducers are designed to meet the needs of the applications in general purpose and industrial grade with pressures up to 15,000 PSIG.

The Electrical Output of Pressure Transducers
FTB Pressure transducers are available with two types of electrical output; volt with 0-5 VDC or 0-10 VDC, and 4-20mA. We offer transducers with either an industry standard 4-20mA current or 0-5/10VDC voltage output. This signal is linear and proportional to the input pressure. The 4-20mA output signal is the most popular and offers the following advantages: immunity to interference from electrical noise (RFI), low installation cost, and the minimum 4mA signal can be used for diagnostic capabilities. The output signal is sent to computers, PLC's, chart recorders, digital panel meters, or other devices that interpret this signal and use it to display, record and/or change the pressure in the system being monitored. Below is a summary of the outputs and when they are best used.

1) 0-5 or 0-10 Voltage Output Pressure Transducers
Voltage output transducers include integral signal conditioning which provide a much higher output than a millivolt transducer. The output is normally 0-5Vdc or 0-10Vdc. Although model specific, the output of the transducer is not normally a direct function of excitation. This means unregulated power supplies are often sufficient as long as they fall within a specified power range. Because they have a higher level output, these transducers are not as susceptible to electrical noise as millivolt transducers and can therefore be used in much more industrial environments.

2) 4-20 mA Current Output Pressure Transducers
These types of transducers are also known as pressure transmitters. As a transducer produces millivolts, amplified voltage, or current output, a transmitter produces current output only. Since a 4-20mA signal is least affected by electrical noise and resistance in the signal wires, these transducers are best used when the signal must be transmitted long distances. It is not uncommon to use these transducers in applications where the lead wire must be 1000 feet or more.

Pressure Ranges
FTB transducers are fixed range. The range selected is determined by the application requirements. The standard range should ALWAYS be greater than the highest expected working pressure generated by the application. The most recommended range for the application is 2 times of the working pressure. Basic pressure references are as follows:
Vacuum transducers are vented to atmosphere and produce a 4 mA output when no vacuum is applied. The output increases as the vacuum applied increases (20 mA maximum).
Gauge Pressure transducers are referenced to atmospheric pressure. With no pressure applied, the output is 4 mA or 0 VDC. Gauge pressure transducers usually refer to the pressure range as just PSI (pounds per square inch) or PSIG (PSI gauge) and are the most common transducers.

Maximum Pressure
The maximum pressure defines the safety margin of pressure the transducer can tolerate (for short periods of time) without damage.

Burst Pressure
The maximum pressure causing permanent, nonadjustable damage or destruction of the transducer.

Supply Voltage or Excitation
All transducers require an input voltage in order to power the internal circuitry. The standard optimal input voltage is 5-24 VDC (amplified voltage output transducers) 8-30 VDC (4-20 mA current output transducers), although any voltage within the published range will work. Our transducers feature a built in power regulation circuit, an unregulated power supply in between 5-24 VDC or 8-30 VDC is acceptable. It is strongly recommended using a regulated power supply of 24 VDC on amplified voltage output transducers to maintain the best accuracy of the transducer. If an unregulated power supply in between 5-23 VDC is applied, the accuracy of the transducer will be slightly different from what an 24 VDC regulated power is supplied. For minimum voltage required for current 4-20 mA output transducers, please refer to for details.

Calibration
FTB transducers feature on board zero adjustment for recalibration as required for maintenance procedures on both Industrial Grade and General Purpose transducers.

Pressure/Process Connection
Transducers are available in several types of process connections including NPT (national pipe thread), flush mount diaphragm, 3A sanitary 1.5 or 2 inch Tri-Clamp or submersible with vented cable. NPT connections are for use with non-clogging pressure media only. When measuring media that is viscous, crystallizing, or contains particulates a flush diaphragm type transducer, or a transducer with a chemical diaphragm seal should be installed to protect the transducer. The transducer with a chemical diaphragm seal is commonly used in food and pharmaceutical applications.

Electrical Connection
Our transducers are shipped with an easy-to-install wiring (3 wires). The wiring is therefore connected directly to the wiring of the application.

Accuracy & Performance
Accuracy of the pressure transducer is one measure of performance and includes the following:
Linearity is the error defined by the maximum deviation of a transducer output from a best fit straight line (BFSL) during any one calibration cycle. This is measured as a percent of span. An accuracy of +/- 0.25% BFSL is equivalent to +/- 0.50% terminal point accuracy for calibration purposes. Ex. A 0-100 PSI unit with a +/- 0.25% BFSL accuracy could deviate up to +/- 0.50 PSI terminal point throughout its working pressure range.
Hysteresis is the error defined by the maximum measured separation between the upscale and the downscale indications of the measured pressure during a full range traverse from 0 to the maximum pressure.
Repeatability is the error defined by the ability of a transducer to reproduce an identical signal when the same pressure is applied to it consecutively, under the same conditions and in the same direction. In industrial applications, repeatability is usually the most important specification.
Response Time is the length of time required for the output to change in response to a pressure change.
FTB transducers are all with 1% F.S. (full scale) accuracy.

Temperature
Media Temperature is the maximum allowable temperature of the pressure media being measured without causing damage to the transducer. For steam applications, consider using a steam siphon to reduce the media temperature.
Ambient Temperature is the maximum allowable temperature around the case of the transducer without causing damage.
Temperature Compensation is the range in which temperature changes will cause an output change no greater than the temperature error. However, all FTB-patented transducers are FREE from Temperature Compensation. There will have NO output change caused when the temperature changes. This makes FTB transducers more reliable over the ones available on market.

Pressure Fluid Composition
Since the sensing element of a pressure transducer may be exposed directly to the measured medium, consider the characteristics of this medium. It may be corrosive, it may solidify at various temperatures, or it may contain solids that will clog or leave deposits inside the sensing element. All FTB transducers have 316 stainless steel wetted parts and are for use with pressure fluids that will not solidify (non clogging) under normal conditions or leave deposits. Chemical diaphragm seals or flush diaphragm transducer are typically used to isolate transducers from viscous, corrosive, high temperature, or media containing particulates. Optional brass fitting transducers are also available upon request.

Electrical Protection
FTB transducers are protected against reverse polarity, short circuit output and incorporate a suppressor diode for high-voltage protection.

Shock & Vibration Resistance
Excessive vibration can damage transducers. Whenever possible, the user should try to install the transducer in an area that minimizes vibration. Vibration specifications on FTB transducers are among the best in the industry.

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