Could you tell what HART means ? For example the 1794-OE8H. What is the difference ?

[Baker in Virginia]

Good Morning ,

I am looking to modify a machine , and I am looking at using Rockwell Automation Flex I/O modules . I ne a few analog output modules , and I want a output module with the most outputs on one module. I took notice the 1794-OE8H has 8 outputs. But I took notice that it says HART on it. I have seen that alot. Is HART a manufacture or a method of circuitry in the module. I imagine they wire the same , correct ?

Thanks in advance ,

 

[scott.lawrence]

HART is a protocol

https://en.wikipedia.org/wiki/Highway_Addressable_Remote_Transducer_Protocol


it allows communications across an analog signal that gives more data than just the analog value

 

[JohnCalderwood]

is there not a 1794-OE12 available?

 

[labeledas]

simply put HART is a digital overlay on your 4-20mA analog signal. A non hart device will still send its signal as normal, however using a HART compatible device "smart device" will allow you to access other features and parameters

 

[Baker in Virginia]

Thanks . I think I understand . I am still confused how you can separate the signals at the controller . I didn't see the 1794-OE12 in the Flex I/O list , but I did search for it and found it . Thanks for the tip and info .

 

[labeledas]

What do you mean by separate.

It is one signal with a frequency shifted overlay. Like a ripple on your 4-20mA if the controller if you have a hart transmitter going to a hart card.

The TX can send out pulses, so let's say yout TX is running at 12mA it will actually go between 11.5 and 12.5 at 1200hz for a 1 and 2200hz for a 0. This way the tx can send out binary streams like 01100110110 or whatever by shifting the ripple frequncy between those 3 values. a hart meter or plc card normally issues a command, since it is master slave protocol, and is looking for a response made up of these shifts and can understand them a non hart card or meter would never send a command but ifbthe tx didntry to talk to it, it will only see the 12mA since it is the average of the 11.5-12.5 ripple and it is missing the circuitry to interpret the signal

Likewise if your hart card or meter tries to send a command to a non hart TX it ignores it since it is not looking for it.

 

[danw]

A HART card ALWAYS has 4-20mA. You can use only the 4-20mA (and ignore the HART) if there is no need for HART communication.

It takes additional firmware/software to deal with HART values. The 4-20mA is standard 4-20mA.

 

[ndzied1]

Here is a pretty good description of HART
https://youtu.be/JL9ev5yElK4

 

[Geospark]

Thanks . I think I understand . I am still confused how you can separate the signals at the controller . I didn't see the 1794-OE12 in the Flex I/O list , but I did search for it and found it . Thanks for the tip and info .

If by "separate" you are more referring to distinguishing the HART data in the controller from the analog data -
when you enable HART for the module's channels, extra module-defined tags will be automatically created at the Controller-Scope specifically for the HART data.

I'm not going any further into describing that data and its uses as I'm pretty sure you're not that invested in using this particular feature. The 1794-OE12 should better suit your needs, I'd imagine.

However, I am curious...

When you say "modify a machine", and that you are "looking at using Rockwell Automation Flex I/O modules", are you saying that you must use Flex I/O here because the existing machine uses it, or it is a preference that you have, regardless of what is already in use? It's just that if it is the latter here, then there may be better or more modern options available to you.

Regards,
George