Absolute pressure transmitters measure the difference between vacuum and measured pressure. Absolute pressure (AP) transmitter is a measure of the ideal (complete) vacuum.

Absolute pressure transmitters, also known as absolute pressure transducer,
and absolute pressure sensor. Measure absolute pressure relative to full vacuum. In contrast, pressure measured relative to atmosphere is called gauge pressure. All absolute pressure measurements are positive. The readings produced by absolute pressure sensors are not affected by atmosphere. When the pressure corresponds to the ideal vacuum, the absolute pressure transmitter will produce a 4mA output signal.

Sino-Inst offers a variety of pressure senors for industrial pressure measurement. If you have any questions, please contact our sales engineers.

Absolute Pressure Transmitter Features

Direct Mount Pressure-Absolute Pressure Transmitter
Direct Mount Pressure-Absolute Pressure Transmitter
  • Sensor Type : Industrial Pressure Transducers
  • Full function buttons on site
  • Pressure ranges: 0 … 1 mbar up to 0 … 600 bar
  • Output/Span 0 – 10 V, 0 – 5 V, 1 – 5 V, 10 mV/V, 4 – 20 mA, HART
  • Pressure Port/Fitting : 1/2 MNPT, 1/4 FNPT, 1/4 MNPT, 1/8 MNPT
  • Operating Temperature Range: -40 – 85 °C [ -40 – 185 °F ]

Extended reading: How to calibrate HART pressure transmitters

Specifications of Absolute Pressure Transmitter

ModelTransmitter type
SI-1301GPPressure transmitter
SI-1301APAbsolute pressure transmitter
CodeScale range
CodeOutput form
ELinear output 4-20mAdc
SFLinear output 4-20mAdc+HART signal,Full function buttons on site
FMODBUS-485 signal
CodePressure connection
L11/4NPT-18 Internal thread (excluding waist joint standard)
L21/2NPT-14 Internal thread
L3M20×1.5 External thread
CodeOptional parts
M4LCD multi – power digital display head
B1Pipe bending bracket
B2Plate bending bracket
B3Pipe mounting bracket
D0The discharge valve is at the end
D1The side discharge valve is on the upper part
D2The side discharge valve is on the upper part
C02M20 x 1.5 nut and Φ 14 pressure short tube
C121/2NPT-14 external thread and Φ14 pressure short tube
C221/4NPT-18 external thread and Φ14 pressure short tube
C321/4NPT-18 to M20×1.5 external thread
C421/2NPT-14 to M20×1.5 external thread
C431/2NPT-14 to 1/4NPT-18 internal thread
C441/2NPT-14 to 1/2NPT-14 external thread
C451/2NPT-14 to G1/2 external thread
X1Oil ban
GdMeasure the gold-plated membrane box
DaFlameproof  ExdIIBT5Gb;(explosion-proof certificate no. : CE16.1163)
FaIntrinsically safe ExiaIICT4 / T5 / T6Ga;(explosion-proof certificate no. : CE15.2354X)
CodeFlange connectorExhaust/Drain valveIsolation diaphragmFilling liquid
22316 Stainless steel316 Stainless steel316 Stainless steelSilicone oil
23316 Stainless steel316 Stainless steelHastelloy CSilicone oil
24316 Stainless steel316 Stainless steelMonelSilicone oil
25316 Stainless steel316 Stainless steelTantalumSilicone oil
33Hastelloy CHastelloy CHastelloy CSilicone oil
35Hastelloy CHastelloy CTantalumSilicone oil
44MonelMonelMonelSilicone oil
CodeShell materialConduit inlet dimensions
ALow copper aluminum alloy polyurethane coatingM20×1.5
BLow copper aluminum alloy polyurethane coating1/2-14 NPT
CStainless steelM20×1.5
DStainless steel1/2-14 NPT

Read more about: Common Units Of Pressure

What is the absolute pressure? 

The pressure acting on the surface of object is called “absolute pressure”. The absolute pressure value starts with absolute vacuum.

The absolute pressure sensor measures the pressure relative to the high vacuum reference. The high vacuum reference is sealed behind its sensing diaphragm. The vacuum must be negligible compared to the pressure to be measured.

Sino-Inst’s absolute pressure sensor provides a pressure range of 1 bar or even 700 mbar. Most electronic pressure sensors measure pressure based on the deformation of the diaphragm.

For Gauge pressure sensors, One side of the diaphragm is exposed to process pressure, while the other side is exposed to ambient. This means that the pressure is actually the difference between the process pressure and atmospheric.

For absolute pressure sensors, the side of the sensor that is not in contact with the pressure medium is exposed to a permanently sealed absolute vacuum chamber. The deformation of the diaphragm is not affected by atmospheric. Because it uses a sealed vacuum as a reference point and zero point.

What is absolute pressure transmitter?

Absolute pressure (AP) transmitter measure relative to perfect (full) vacuum pressure (absolute zero pressure).

Therefore, AP transmitters are not affected by fluctuations in the local atmosphere.

All absolute pressure measurements are positive.
The letter ‘a’ or the abbreviation ‘abs’ in the unit of measure
(i.e., inH₂O(abs) or psia) indicates an absolute pressure measurement.

Any critical storage and delivery (toxic gases) will change due to atmospheric conditions. So these systems must be accurate and use static references. Absolute pressure transmitters are used in applications where the pressure of a gas or liquid is isolated from changes in atmosphere. For example, when testing a sealed pressure vessel for leaks for a long time.

How do absolute pressure sensors work?

The absolute pressure transmitter is mainly composed of two parts. One part is directly connected to the side to be measured. The other side is designed as an absolute vacuum reference chamber. This makes the two compartments form Absolute pressure. When the pressure on both sides is inconsistent, the difference signal will be transmitted through a special transmission line. The computer system in the background can calculate the difference. The pressure value on the measured side is directly displayed.

Applications for Absolute Pressure Sensors

Absolute pressure sensors and absolute pressure gauges are commonly used in industrial high-performance vacuum pumps that require monitoring.

For example, it is used to vacuum package medical products in a clean environment. To ensure that hospitals and doctors are provided with hygienic and bacteria-free delivery.

In the food industry, when the highest possible vacuum is needed to prevent oxygen from degrading perishable food, vacuum packaging can be used, which greatly extends the flavor and shelf life of the product.

For example, in meat packaging, a vacuum that meets the requirements must be generated, so that the longest shelf life can be safely guaranteed.

Pressure sensors affected by the atmosphere cannot monitor the high end of the vacuum.

Applications that require true absolute pressure sensors and gauges can also be found in scientific laboratories, universities, military and aerospace industries.

Applications requiring true absolute pressure sensors and gauges, can also be found in scientific laboratories, universities, the military, and the aviation industry.

Sino-Instrument supplies Direct Mount Pressure / Absolute Pressure Transmitter.

SMT3151 Absolute Pressure Transmitter
SM3151TGP-TAP Pressure-absolute pressure transmitter shape and installation dimensions
SM3151 TAP Pressure-absolute pressure transmitter shape and installation dimensions

Absolute pressure transmitter calibration

  1. First make a 4-20mA fine adjustment. It is used to calibrate the D / A converter inside the transmitter. Because it does not involve sensing components, no external pressure signal source is required.
  2. Do a full fine-tuning again. Make the 4-20mA, digital reading coincide with the actual applied pressure signal. Therefore, a pressure signal source is required.
  3. Finally, re-quantify the range. By adjusting the analog output 4-20mA and the external pressure signal source. Its function is exactly the same as the zero (Z) and range (R) switches on the transmitter shell.

Gauge pressure VS absolute pressure

1. Gauge pressure:

Gage pressure refers to pipeline pressure. It refers to the pressure measured with pressure gauges, vacuum gauges, U-shaped tubes and other instruments. It is also called relative pressure. “Gage pressure” starts from atm.

2. Absolute pressure:

The pressure directly acting on the surface of the container or object is called “absolute pressure”. The absolute pressure value starts with absolute vacuum.

3. Relationship:

Absolute pressure actually refers to the gauge pressure plus the local atm.

Absolute pressure = gauge pressure + 1 atm

If it is in MPa, absolute pressure = gauge pressure + 0.1MPa

Gauge pressure = absolute pressure-atm

Vacuum = atm-absolute pressure

The pressure measured on the basis of absolute vacuum is the absolute pressure. The pressure measured on the basis of atm is the gauge pressure or the degree of vacuum. G behind the pressure indicates gauge pressure, A indicates absolute pressure.

The gauge pressure g = gauge refers to the pressure indication of the pressure gauge on the system. It can also be simply understood as putting a pressure gauge under atm, at which time the pressure gauge displays zero. The gauge pressure at this time is displayed as 0. If the pressure of this gauge pressure rises, the rising value is the gauge pressur

Read more about: Absolute Pressure Vs Gauge Pressure Measuring Instruments

Absolute pressure transmitter VS Gauge pressure transmitter

Absolute pressure transmitter

Absolute pressure transmitter can realize absolute pressure measurement in equipment such as degassing system, distillation tower, evaporator and crystallizer, and allows pressure under 10Mpa. The δ chamber side of the absolute pressure transmitter receives the measured absolute pressure signal. The other side is sealed into a high vacuum reference chamber. Then convert it into 4 ~ 20mA DC signal output.

Gauge pressure transmitter

A gauge pressure transmitter in the general sense is mainly composed of a load cell sensor (also called a pressure sensor), a measurement circuit and a process connection. It can convert the physical pressure parameters such as gas and liquid felt by the load cell sensor into standard electrical signals (such as 4 ~ 20mADC, etc.), and provide secondary indicators such as alarm indicators, recorders, and regulators for measurement and indication. And process regulation.

Sino-Inst is Chinese manufacturer of absolute pressure transmitters.

SMT3151ap absolute pressure transmitters, are our mian products, which are widely used in India, US, South Africa, and other countries.

Contact us any time, if you need the quotation or technical support.

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