Beckhoff Remote IO and Unitronics V280

My latest experiment is now in the downloads section, fully functional and ready to roll!

I got a sample unit from Beckhoff of their CompactBox remote IO. This is IP67 rated modbus serial remote IO, 2-wire RS485. The particular unit is IP2301 B730-0000.

I connected this to a Unitronics Vision 280 using the RS485 option card for a third comm port (I had one lying around). I did NOT use termination - you may do so if you need/wish to. I connected my card to pins 2 and 4 of the beckhoff, supplied 24VDC to everything, and made a test plug for the inputs.

The program includes a display screen to show active inputs and outputs. Address on the beckhoff is 02, with NO other configuration changes - as she roared from the box, so she roars today.

The unit is a little pricey. $250 base, with all plugs from my vendor, cost is about $440. Some of this is offset by what you don't have to buy - enclosures, relays and terminals, and miles of wire.

Now, consider that it took longer to write the code than to hook it up on my tabletop, and the labor cost savings should make it at least break even. I haven't crunched the numbers for a real project yet, but I suspect I'll even save money.

Download it and give it a look!

TM

Here's an update from the battlefront:

I decided to run some latency tests by loop-back. I programmed the V280 2.5mS interrupt routine to time how long it took, from the time I pressed the "0" key on the keypad, turning on remote output 0, until I read back remote Input 0. I wired the output directly to the input and tested it at 9.2Kbaud and 38.4 Kbaud.

This takes full account of all latency in the system, including plc scans, transmission time, and reaction time of the module. I'm not sure what to make of the results since I've never benchmarked like this before, so here is the data :

9.2 kbaud latency, 10 tests:
Average: 112.5 mS
Minimum: 77.5 mS
Maximum: 147.5 mS

38.4 kbaud latency, 10 tests:
Average: 70 mS
Minimum: 45 mS
Maximum: 85 mS

Most likely, modbus TCP will be faster, although I cannot say by how much, since I cannot say how much of the total latency is owing just to transmission rates.

I am curious to know what latencies other people have seen on remote IO networks. Anybody wanna share?

Thanks!

TM

By way of comparison, I just performed the same latency test on the system I currently have running, which uses an M91 as remote IO. The results were not unexpected:

38.4Kbaud, ten samples
Average : 127 mS
Minimum : 100 mS
Maximum : 145 mS

The M91 at 38.4Kb was slower than the Beckhoff at 9.2Kb. I attribute this to the need of the M91 to execute scans and generate a reply packet. The beckhoff does not face this additional overhead.

Next up, ethernet... if I can find a #%$%^ patch cord...

TM