Several issues with the HART protocol
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1. Smart meters equipped with the HART protocol, such as Rosemount pressure transmitters, can use the 475 standard to communicate via digital signals superimposed on analog signals; this enables remote zero-point and range adjustment, fault diagnosis, and even configuration. However, we still use a 2-wire system to transmit 4–20 mA signals to the DCS. 2. My understanding is that if it is switched to bus-based control in the future, it would be possible to avoid replacing the transmitter, by converting the 4–20mA analog signal into a digital signal right within the transmitter and then sending it to the DCS via the bus. 3. For simple remote calibration, I think smart meters (transmitters) are an overkill – ordinary meter faces with LED displays can also be calibrated on-site, yet the price difference isn’t minimal at all.
It’s not that simple. If you opt for a fieldbus, then all the current transmitters and AI cards must be replaced with bus cards that use the same protocol
Now that the field instruments come equipped with HART functionality, it is possible to read and modify their status and parameters from the control room using the DCS system (which is supported by most modern DCS systems). This does not cause any conflicts with 4–20 mA signals, which greatly simplifies the work for instrument maintenance personnel. If it is changed to a bus format, as mentioned above, the original card components will no longer be usable; it will be necessary to install bus signal reception cards that use the same protocol. For systems that did not originally have such components, it seems unnecessary to make any changes. For newly installed devices, it is necessary to consider whether to use single-point transmission or bus transmission, a decision that is made based on comprehensive design considerations.
I don’t know that much about it; it seems that Hart’s functions are only used in a limited number of ordinary transmitters, as most of Hart’s features aren’t utilized. Some higher-end transmitters seem to make more use of these functions. As for what you mentioned regarding the possibility of converting without replacing the gauge, regarding what the friends above said about the need to replace the card module, I’ll tell you in private that the gauge still needs to be replaced as well – the gauge itself does not support such a function. But I’ll also tell you in private that for gauge manufacturers, Hart output and bus output are just different types of output boards; everything else remains the same. However, for users, the gauge still has to be replaced. Meters with on-site buttons allow only adjustment of a very limited number of common functions; most functions cannot be implemented, so it’s still more convenient to use 475
Oh! So in other words, the instruments equipped with HART cannot be used on buses at the moment; they are transitional products, similar to PHS phones. Once smartphones become more widespread, they will be phased out, right?
Oh! So in other words, the instruments equipped with HART cannot be used on buses at the moment; they are transitional products, similar to PHS phones. Once smartphones become more widespread, they will be phased out, right?
For example, if you are currently using HART (an analog-to-digital transitional bus protocol) and plan to switch to FF (a fully digital protocol), then your transmitters also need to be changed to FF type, and the original AI cards must be replaced with bus-type cards as well. Hehe
HART is a basic form of bus (similar to 2.5G mobile communication technology). The FF bus incorporates data processing and simple PID control modules within the FF transmitter, something that HART cannot do. Transmitters on the PROFIBUS bus do not have a control module; the control function is implemented in the controller. HART uses a very low signal frequency (1.2 KHz), operates in a master-slave configuration (similar to MODBUS RTU), is slow, and while the information it provides is acceptable, it is not suitable for control purposes. The low-speed network of the field bus reaches a rate of 31.25 K. This is merely a difference at the physical layer; there are also a whole set of standards such as the data exchange layer that support bus technology, and HART pales in comparison to these. @jiaguoyun
The original poster’s thinking is rather superficial; it’s not that simple actually – there are differences between FF and HART. Liquid crystal displays cannot enable intelligent management of instruments across the entire plant.
1. Hart’s problems are, first, slowness, and second, the issue that all communications face: reliability. 2. To change the analog output of the instrument to a digital output (FF/Profibus/Modbus), it is necessary to replace the component or add a communication board. The data processing inside the transmitter is already in digital form; it is converted to an analog format only for output purposes. Converting it back from analog to digital now is unnecessary, isn’t it? 3. The key to many things lies in the fact of working remotely – why would anyone want to work under the sun, surrounded by noise, and possibly having to climb up and down to the site, when they can simply do the work from an engineer’s station with air conditioning and just by using a mouse?