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Operation of electronics with HART
Function diagram of electronics
- The input pressure is converted into an electrical signal by the sensor.
- This signal is amplified by the measuring amplifier and digitalized in an analog-to-digital converter.
- The digital signal is analyzed in a microcontroller and corrected according to linearity and thermal characteristics.
- In a digital-to-analog converter it is then converted into the output current of 4 - 20 mA. When connected to supply lines, a diode circuit provides reverse polarity protection.
- The measuring cell-specific data, the electronic data and the parameterization data is held in two EEPROMs. One EEPROM is incorporated into the measuring cell electronics, the other is incorporated into the application electronics.
Operation
- The three keys enable you both to navigate and carry out parameterization and to visually track messages and process values, provided a display is available.
- If you have a device without a display, you can carry out zero adjustment using the keys. It is possible to retrofit a display at any time.
- You can also carry out settings by computer via a HART modem.
Mode of operation of the measuring cells
Measuring cell for differential pressure and flow
Measuring cell for differential pressure and flow, function diagram
- The differential pressure is transmitted via the seal diagrams and the filling liquid to the silicon pressure sensor.
- If the measuring limits are exceeded, the overload diaphragm flexes until it makes contact with the body of the measuring cell. This protects the sensor model from overload.
- The differential pressure causes the measuring diaphragm of the silicon pressure sensor to flex.
- The displacement changes the resistance value of the 4 piezo resistors in the measuring diaphragm in a bridge circuit.
- The change in the resistance causes a bridge output voltage proportional to the input pressure.
Measuring cell for level
Measuring cell for level, function diagram
- The input pressure (hydrostatic pressure) acts hydraulically on the measuring cell via the seal diaphragm on the mounting flange.
- The differential pressure applied to the measuring cell is transmitted via the seal diaphragm and the filling liquid to the silicon pressure sensor.
- If the measuring limits are exceeded, the overload diaphragm flexes until it makes contact with the body of the measuring cell. This protects the silicon pressure sensor from overload.
- The differential pressure causes the measuring diaphragm of the silicon pressure sensor to flex.
- The displacement changes the resistance value of the 4 piezo resistors in the measuring diaphragm in a bridge circuit.
- The change in the resistance causes a differential pressure proportional to the input pressure.
Parameterization of SITRANS P500 HART
Depending on the version, there are a range of options for parameterizing the pressure transmitter and for setting or scanning the parameters.
Parameterization using the input keys (local operation)
You can parameterize the transmitter in situ using the three keys provided a display is available. If you have no display, you can only carry out zero adjustment.
It is possible to retrofit a display. See accessories.
Parameterization using HART
Parameterization using HART is carried out using a HART Communicator or a PC in conjunction with a HART modem.
Communication between a HART Communicator and a pressure transmitter
When parameterizing with the HART Communicator, the connection is made directly to the 2-wire cable.
HART communication between a PC communicator and a pressure transmitter
For parameterizing via PC a HART modem is used which connects the transmitter to the PC.
The signals needed for communication in conformity with the HART 6.0 protocols are superimposed on the output current using the Frequency Shift Keying (FSK) method.
The necessary device files are available for download on the Internet.
SITRANS P500 parameterization options
The transmission offers you full parameterizing options both via HART as well as in situ provided the optional display is available.
For simple parameterizing we also offer the easy to understand QuickStart function with guided commissioning.
SITRANS P500 diagnostic functions
- Maintenance timer
- Slave pointer (can be reset/cannot be reset)
- Pressure (incl. time and temperature)
- Static pressure (incl. time and temperature)
- Sensor temperature (incl. time stamp)
- Electronic temperature (incl. time stamp)
- Limit transmitter
- Diagnostics warning
- Diagnostics alarm
- Simulation functions
- Display of trends and histograms
- Operating hours meter
Physical dimensions available for the SITRANS P500 HART display
|
Physical variable |
Physical dimensions |
|
Pressure (setting can also be made in the factory) |
Pa, MPa, kPa, bar, mbar, torr, atm, psi, g/cm2, kg/cm2, mmH2O (4 °C), inH2O (4 °C), inH2O (20 °C), mmH2O, mmH2O (4 °C), ftH2O (20 °C), inHg, mmHg, hPA |
|
Level (height data) |
m, cm, mm, ft, in |
|
Volume |
m3, dm3, hl, yd3, ft3, in3, gallon, lmp. gallon, bushel, barrel, barrel liquid, I; Norm (Standard) I; Norm (Standard) m3, Norm (Standard) feet3 |
|
Mass |
g, kg, t (metric), lb, Ston, Lton, oz |
|
Volume flow |
m3/d, m3/h, m3/s, l/min, l/s, ft3/d, ft3/min, ft3/s, US gallon/min, gallon/s, l/h, milL/d, gallon/d, gallon/h, milgallon/d, lmp.gallon/s, Imp.gallon/m, Imp.gallon/h, lmp.gallon/d, Norm (Standard) m3/h, Norm (Standard) l/h, Norm (Standard) ft3/h, Norm (Standard) ft3/m, barrel liquid/s, barrel liquid/m, barrel liquid/h |
|
Mass flow |
t/d, t/h, t/min, kg/d, kg/h, kg/min, kg/s, g/h, g/min, g/s, lb/d, lb/min, lb/s, LTon/d, LTon/h, STon/d, STon/h, STon/min |
|
Temperature |
°C, °F |
|
Miscellaneous |
%, mA |