25-08-2017, 09:32 PM
PRESSURE TRANSMITTER
PRESSURE.ppt (Size: 659 KB / Downloads: 55)
Types of pressure
Static Pressure:
Force (Potential Energy) acting per unit area is known as Static Pressure .
Pressure in moving fluids (Dynamic Pressure)
The pressure in a moving fluid exerted parallel to the flow direction is called the impact pressure, PI. This isdue to the kinetic energy of the fluid.
Pressure measurement
Absolute pressure:
It is measured relative to a perfect vacuum. An example is atmospheric pressure.
Differential pressure:
It is the difference in pressure between two points of measurement.
Gauge pressure:
It is measured relative to ambient pressure. Blood pressure is one example.
Pressure Sensing Technology
Inductive Pressure Sensors
Capacitive Pressure Sensors
Piezoelectric Pressure Sensors
Transmitter Measuring Principle
The diagram shows an electronic differential pressure sensor. This particular type utilizes a two-wire capacitance technique.
The differential capacitance between the sensing diaphragm and the capacitor plates is converted electronically to a 4–20 mA or 1-5 VDC signal.
For a gauge pressure transmitter, the low pressure side is referenced to atmospheric pressure.
HONEYWELL ST 3000
ST 3000 Pressure Transmitter proven “smart” technology to a wide spectrum of pressure measurement applications, from furnace combustion airflow rate to hydrostatic tank gauging.
All ST 3000 transmitters provides
4-20 mA output
Honeywell Digitally Enhanced (DE) output
HART output, or FOUNDATION Fieldbus output
Honeywell’s cost-effective ST 3000 transmitters lead the industry in reliability and stability
Stability = +/-0.01% per year
Reliability = 470 years MTBF
Description
The ST 3000 transmitter can replace any 4 to 20 mA output transmitter in use today, and operates over a standard two-wire system.
The measuring means is a piezoresistive sensor, which actually contains three sensors in one.
It contains a differential pressure sensor
Temperature sensor and
static pressure sensor
It Works on the principle of 2-Wire Capacitance.
Pressure transmitter selection guideline
When selecting a pressure transmitter care should be given to a number of parameters which have an effect on transmitter accuracy, safety, and utility.
Accuracy required
Power supply
Operating pressure range
Operating temperature range
Body Material
Pressure fluid composition and Internal parts
Mounting requirement