发表于：2004/8/10 15:07:00
#0楼
Is calibration necessary for digital fieldbus devices?
Calibration is often associated with analog devices. It's therefore sometimes assumed that digital fieldbus devices don't need to be calibrated. Many do.
With analog devices, calibration compensates for inaccuracies in three parts of the device:
* Sensor or actuator
* Device electronics
* Analog communications signal.
Fieldbus devices have no analog communications signal, eliminating that source of error. However, on many devices the sensor or actuator, and the device electronics, can have errors. So calibration is still sometimes required.
With an analog device, such as a transmitter, the output is scaled so that the expected operating range uses the entire 16 mA of a 4-20 mA signal. This minimizes the effect of error in both the transmitter analog output and the host analog input. However, it's common to see errors resulting from a mismatch between the scaling of the field device and the host.
With digital fieldbus devices, output scaling isn't required — so there's no such mismatch. Fieldbus does require that the unit of measure be the same in both the device transducer block and the function blocks.
Calibration is often associated with analog devices. It's therefore sometimes assumed that digital fieldbus devices don't need to be calibrated. Many do.
With analog devices, calibration compensates for inaccuracies in three parts of the device:
* Sensor or actuator
* Device electronics
* Analog communications signal.
Fieldbus devices have no analog communications signal, eliminating that source of error. However, on many devices the sensor or actuator, and the device electronics, can have errors. So calibration is still sometimes required.
With an analog device, such as a transmitter, the output is scaled so that the expected operating range uses the entire 16 mA of a 4-20 mA signal. This minimizes the effect of error in both the transmitter analog output and the host analog input. However, it's common to see errors resulting from a mismatch between the scaling of the field device and the host.
With digital fieldbus devices, output scaling isn't required — so there's no such mismatch. Fieldbus does require that the unit of measure be the same in both the device transducer block and the function blocks.