We have a new flow application with an input that needs a pressure device and a temperature device. What I don't get is how it works. How can you read data from two devices on the same cable? Don't I need two inputs instead of one?
Expert’s answer: Multidrop – Can you connect two devices to the same input?
Ehhh, you didn’t give me a whole lot to go on for an accurate answer. But I can explain how it generally works based on devices out there with similar features. You’ll likely connect the flow meter to the other devices with multidrop communication.
People use to say that multidrop is pure HART – no analog, just digital. But to do it, you need to set up the pressure and temperature transmitters on different polling addresses. Then the flow meter will work as a master to read the HART data from them, pulling about two messages a second.
Today, other solutions on the market use multidrop as well. The wireless adapter saves energy to power devices, if you set the communication as multidrop and skip the analog.
And some HART displays can show more than one process variable. With the multidrop, you can have two different masters, primary and secondary. These displays can work in either; you just need to set them up.
If you want to learn more about HART communication, then take a look at these links:
General information about a HART communicator and what does it do.
If you need to decide a field network protocol, here are the advantages of HART.