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How to calibrate smart transmitters with digital outputs

A ‘Smart’ Transmitter is the same as a conventional transmitter in that it senses a physical parameter in a process application and generates an output signal proportional to the measured input. The difference is that whereas a conventional transmitter would generate an analogue signal, a ‘Smart’ transmitter would have a digital communication protocol that can be used for reading the transmitter’s measurement values and for configuring various settings in the transmitter.

For engineer’s who need to configure and calibrate the transmitter, the digital communication protocol makes the biggest difference. Engineers can no longer simply measure the output analogue signal – they need to be able to communicate with the transmitter and read the digital signal.

Rosemount Transmitter

Calibration of Smart Transmitters

Firstly, what exactly is calibration?

According to international standards, calibration is a comparison of the device under test against a traceable reference instrument (calibrator) and documenting the comparison. Although the calibration formally does not include any adjustments, potential adjustments are often included when the calibration process is performed. If the calibration is done with a documenting calibrator, it will automatically document the calibration results.

Calibrating conventional analogue transmitters

To calibrate a conventional, analogue transmitter, you can generate or measure the transmitter input and at the same time measure the transmitter output. In this case calibration is quite easy and straight forward; you need a dual-function calibrator able to process transmitter input and output at the same time, or alternatively two separate single-function calibrators.

Calibrating a smart transmitter with digital output

But how can a smart transmitter, with output being a digital protocol signal, be calibrated?

Obviously the transmitter input still needs to be generated/measured in the same way as with a conventional transmitter, i.e. by using a calibrator. However, to see what the transmitter output is, you will need some device or software that is able to read and interpret the digital protocol. The calibration may, therefore, be a very challenging task; several types of devices may be needed and several people required to do the job. Sometimes it is very difficult or even impossible to find a suitable device, especially a mobile one, which can read the digital output.

What about calibrating HART Transmitter?

Wired HART (as opposed to WirelessHART) is a hybrid protocol that includes digital communication superimposed on a conventional analog 4-20mA output signal. The 4-20mA output signal of a wired HART transmitter is calibrated the same way as a conventional transmitter. However, to do any configuration or trimming, or to read the digital output signal (if it is used), a HART communicator is needed.

The Solution: Smart Transmitter with multifunctional Process Calibrator

The new Beamex MC6 is a device combining a full field communicator and an extremely accurate multifunctional process calibrator. With the Beamex MC6, the smart transmitter’s input can be generated/ measured at the same time as reading the digital output. The results can be automatically stored into the memory of the MC6 or uploaded to calibration software.

Beamex smart transmitter with built-in calibration

When it comes to configuration of the smart transmitters, the MC6 includes a full field communicator for HART, WirelessHART, FOUNDATION Fieldbus H1 and Profibus PA protocols. All required electronics are built-in, including power supply and required impedances for the protocols.

The Beamex MC6 can be used both as a communicator for the configuration and as a calibrator for the calibration of smart instruments with the supported protocols. The MC6 supports all of the protocol commands according to the transmitter’s Device Description file. Any additional communicator is therefore not needed.

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