It is reasonable to say that Rosemount fieldbus transmitter series can help customers reduce the overall cost of the system.
In the 4 ~ 20mA communication mode, ordinary Rosemount transmitter series can only measure one physical variable. If this measurement variable is to be converted into necessary data for control, users will need other auxiliary instruments.
For example, when measuring steam flow with temperature and pressure compensation, three Rosemount transmitters are needed to measure temperature, pressure and differential pressure (flow) respectively. While in the fieldbus control system, you just need one fieldbus transmitter.
Using fieldbus transmitter not only simplifies the system structure greatly, but also reduces the comprehensive cost of the system. On the other hand, it also reduces the cost of system installation, debugging and maintenance.
What does the “all digital transmission” of Rosemount fieldbus transmitter mean?
Here’s our explanation.
A fieldbus transmitter uses fieldbus as a kind of digital communication network, which extends from the control room to the production site, so that the point-to-point analog signal transmission in the past is changed into multi-point and one-line serial digital transmission.
Ordinary Rosemount intelligent transmitter has both digital circuit and analog circuit. However, for the fieldbus transmitter, both its sensor circuit and converter circuit are digital. Therefore, the full digital transmission of fieldbus transmitter makes the structure of the transmitter more simple. And its resolution, measurement speed and stability are higher than ordinary Rosemount intelligent transmitters.
Figure 2: Different models of Rosemount transmitters on an industrial expo.
The fieldbus communication mode of Rosemount transmitter is meeting the international standard step by step, which ensures the competence of interoperability of Rosemount transmitter based on fieldbus.
And what is interoperability?
The so-called interoperability of fieldbus transmitter refers to the ability that devices from different manufacturers can communicate with each other and complete tasks in a multi manufacturer environment.
The interoperability of Rosemount fieldbus transmitter enables the devices of different manufacturers to work with each other. As long as the components of a control system meet the international communication standard of fieldbus, they can exchange information with each other, no matter they are produced by which manufacturer.
In this way, users do not have to choose Rosemount fieldbus transmitter around a certain instrument company. Moreover, the Rosemount fieldbus transmitter greatly increases the degree of control system composition, so that users can construct their own control system with the best optimal performance / price ratio.
Rosemount fieldbus transmitter is designed with many excellent features. Here we will introduce one of its benefits - high precision performance.
In ordinary intelligent Rosemount transmitter, some sensors are not directly converted to digital. It puts the pressure difference on the diaphragm to produce displacement, changes the capacitance or resistance, first outputs the voltage, and then converts it into digital signal through the analog-to-digital (A/D) conversion of the transmitter, and afterwards sends it to the microprocessor.
In fact, there are some intelligent Rosemount transmitters, which can directly convert displacement of differential pressure diaphragm into frequency signal, without A/D converter. However, in order to keep 4 ~ 20mA analog signal, D/A converter still exists. Therefore, with the Rosemount intelligent transmitter, its signal transmission accuracy will be reduced in repeated A/D and D/A conversion.
However, there is no A/D and D/A conversion circuit in the field bus Rosemount transmitter, so there is no conversion error between A/D and D/A, so the signal transmission accuracy is improved. Therefore, the accuracy of fieldbus transmitter is higher than that of ordinary intelligent transmitter.
For Rosemount intelligent transmitters and analog transmitters, the signal exists in the continuous form of 4 ~ 20mA, and the change of signal value can be infinitely small. Therefore, in analog signal transmission, noise and signal distortion are unavoidable.
In other words, the stability of analog signal transmission by Rosemount ordinary transmitter is not very good, and the zero point is easy to drift. But for Rosemount fieldbus transmitter, there are only two valid values of the signal: 0 or 1. When the signal is of high electrical level, general noise can hardly distort it. Only if in the presence of large interference, it is possible to distort the signal.
Therefore, to sum up, when transmitting 4 ~ 20mA analog signal, Rosemount fieldbus transmitter has stronger anti-interference ability than intelligent transmitter.
To learn about different Rosemount pressure transmitter series and models (series 1151, 2088, 2051, 3051), please check this article:
Rosemount Transmitter Series 1151, 2088, 2051, 3051CA, 3051S and the Differences