I have a question regarding PLCs and instruments
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Hello, experts. I have a question. It’s like this. One of the testing devices in our laboratory requires data acquisition and control functions. I approached a manufacturer with the request to integrate the data acquisition system and the PLC into a single cabinet. Regarding the selection of instruments and valves, they said that no HART protocol or communication is needed; only a 4-20mA output signal is required in order to enable data acquisition and control functions. The device needs to collect data on temperature, pressure, pressure difference, and flow rate – less than 20 sensors in total. As for control functions, they mainly involve interlock control between electric control valves and the data acquisition system, adjustment of valve opening degrees, and control of pump startup and shutdown. I would like to ask whether this type of small cabinet, as he said, doesn’t require a HART protocol when purchasing instruments Thank you all. I’m not in this field, so I don’t know much about it
The HART protocol is not mandatory, but it facilitates the testing and maintenance of instruments; it depends on your requirements
It’s not necessary to use HART protocol instruments, but most instruments these days are smart instruments. To operate the instrument using the HART protocol, a handheld communicator is also required, which costs tens of thousands of yuan.
In other words, even if a manufacturer can provide this function of digital data acquisition and control regardless of whether HART protocol is available, if I purchase an instrument equipped with HART, first, my costs will increase, and second, it might be unnecessary
This post was last edited by budaoweng123 on 2016-1-25 at 10:34. Transmitters need to be configured using a handheld operator; flow and level measurements are no problem (they are usually configured via the buttons on the gauge), and temperature signals can be fed directly into the temperature measurement I/O module. But what about pressure transmitters? It’s not possible to configure through the table header; it must support either HART or DE protocol.
As mentioned on the fifth floor, some instruments require parameter setting via a handheld controller; in other words, they need to support industrial communication protocols such as HART. Unless the original poster can buy instruments that all come with button settings. On the other hand, a domestic HART 475 costs only 2,000 or 3,000 yuan; the 375 model is being phased out gradually, and it still performs well – there’s no need to purchase Emerson’s models which cost tens of thousands of yuan each.
My instruments are the most basic types: temperature transmitters, pressure transmitters, differential pressure transmitters, and flow meters. The temperature and pressure measurements need to be more precise, but the manufacturer told me that an output signal of 4-20mA is sufficient; all other data acquisition and control functions can be handled through their control panels. I don’t understand the underlying principles, so I’m asking – if this can indeed be achieved, then I won’t need instruments, valves, or flow meters with HART functionality.
Then all the instruments that are connected to the PLC on-site must have button controls; otherwise, you’ll be in trouble once you buy those instruments if they don’t come with control panels and buttons.
HART communication is not a mandatory option, but unless you can determine all parameters such as the measurement range of each instrument and whether flow rates should be squared when making the selection, it will be very troublesome to make changes later on. Smart meters are now being promoted widely; these features bring a lot of convenience to subsequent maintenance, and they represent the trend in the development of smart meters. Through appropriate software and hardware, functions such as remote diagnosis, parameter adjustment, and optimized control can be implemented. It is recommended that the original poster opt for smart meters along with the corresponding software and hardware.
Our company specializes in such PLC control systems; HART communication is not mandatory； Of course, you need to ask them what requirements they have regarding the instruments you choose ； If you are using a smart meter, you don’t need this HART communication ； My personal advice is to use smart meters – they are convenient and hassle-free, and such PLCs are not difficult to work with.