Which is faster....Bluehose vs. Analog?

[bdn2004]

We are trying to upgrade the monitoring of our new system. The Vendor supposedly has made it possible to retrieve all of the data via "bluehose". I notice many of the signals that we want are also wired out to analog outputs. It certainly looks like we can get more info from the bluehose. We have a screen in our control room that displays important infor.

I say supposedly because I don't understand how you extract the info from the bluehose. I'm not a programmer.

 

[IRstuff]

Not a question of programming; it's a question of protocol and precision. Assuming 16 bits per data word, 3 mbps Bluetooth would support 200k data words per second, which must be shared amongst all the data streams. For most industrial applications, this is more than adequate. However, an analog data channel is only limited by its internal data bandwidth, but you must protect against noise, offsets, common mode, etc.

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[danw2]

Blue hose is the physical cable used for Allen Bradley's Data Highway and DH+ serial transport layer. I don't know the throughput rates for either, but I doubt that it's bluetooth 3Mb rates.

The 'screen' in your control room can not handle analog data (nor can anyone else's), the HMI panel can only handle digital data.

Presumably both your PLC and the HMI panel screen 'speak' DH or DH+ or some other digital protocol that runs over bluehose cable.

 

[IRstuff]

oh, my bad, I just assumed it was some sort of slang for BT. According to:

http://www.belden.com/products/industrialcable/data-highway.cfm

You could get substantially better than BT, if the distance was sufficiently short. Assuming that the datarates hold true, then BH would definitely provide the smallest footprint solution with the highest effective data throughput. If there are lots of analog, then BH would provide substantial savings in cabling and reduced volumetric overhead for routing a gazillion analog cables.

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[controlsdude]

If you blue hose is configured with an analog card in a remote rack ok but over dh+ slower and less reliable in a big network of plcs.

 

[jraef]

Assuming that the only reason they are choosing DH+ is because of the age of the equipment involved, the data transmission rates are based on RS485, so we are not talking about blazing speed capabilities by today's standards. Typical might be 19.2 kBaud. Still, as a data concentrator of multiple analog signals, that may be better just from a reliability standpoint. But what we don't know here is the speed by which you NEED to see changes in the analog values. Many process applications are so slow anyway that data speed is not critical as long as its in this realm.

If you need faster, and assuming you have an AB PLC5 (by virtue of someone suggesting "Blue Hose"), you may want to consider upgrading your comm modules to Ethernet IP. But first determine what you really need. Assuming faster is better is often a great way to waste money...

"Will work for (the memory of) salami"

 

[djs]

Take any speed estimates with a grain of salt. Most 4-20 ma analog devices will only update their output three times a second (333ms). Many are even slower that that. So even though you may collect data every 100ms, that data is only going to change once every 333ms.

BTW DH+ is RS-485, but DH+ can go up to 230 kbaud. Profibus-DP which is also RS-485 can go up to 12 mbaud.