Netmeter from sst

[Guest Ken Roach]

Has anyone else out there used the NetMeter, which SST sells through their "www.NetAlert.com" subsidary? I was very disappointed with their website initially, but the user manual and the flash movie helped a lot.   My Company's service department had purchased a Synergetic DeviceNet Detective, which I was happy to have but was awfully expensive for us poor little fellows on the sales force. And then yesterday I was working at a tradeshow where the local Brad-Harrison dealer had one.  I went back to the office to get a live DeviceNet demo just so he could run the thing. I'm really impressed with it !   If somebody hadn't swiped the user manual I'd know more, but I was just plain happy seeing the amount of info it was able to show for traffic and CAN errors.   Although you can do a lot of what it does if you have protocol analysis software or a good meter and in-depth knowledge of DeviceNet, this thing fits in your toolbox and looks like a multimeter. Has anyone else out there used the Netmeter?   If you have one, do you use it often or did you shelve it after the startup ?  Do you use other DNet analysis products ?

[Ken Roach 194]

I still haven't gotten one of these for myself, but I borrowed it back from the dealer to explain a question for one of my clients. The client had been installing equipment at a chemical process plant that used 100-DNY42R DeviceNet "starter auxilaries" with in A-B motor control centers.   They had a lot of trouble with a batch of about twenty of them that had come in, saying they'd "crash the network" when installed, or otherwise "just not be recognized".   The verdict of the maintenance manager and my client was that A-B had shipped a bad batch of these devices. The story back at Milwaukee was different.  The QC manager I talked to three months later still had the returned units in a box under his desk.  He'd fired them up, and found nothing unusual except that the Autobaud feature had been turned off and they'd been software-set for 250 kb operation. That explained part of it to me;  the MCCs at the process plant had been set up for 500 kb operation, and when the hard-set starter auxilaries had been plugged in, they'd attempted to communicate at 250 kb, thus stepping all over messages that were running twice as fast, and creating a DeviceNet "Bus Off" condition.    Usually these starter auxilaries come out of the box at 125 kb, but with Autobaud enabled.   When they got purchased under a order with an MCC, though, they probably got hard-set to the data rate for the MCC under which they were ordered.... and then they were installed in a different one. What didn't make sense was that the DSA's sometimes "crashed the network" (read: "caused a Bus-Off condition") and sometimes came up and flashed their network LED's green but weren't detected by RSLinx or by the scanner module. The NetMeter helped explain it to me because I set up a 500 kb network and monitored it for bus errors when I plugged in a DSA set for 250 kb with Autobaud turned off.   About one time out of three, the bus error counter jumped twice, at one second intervals, and then a bus-off occurred.    The other two times, there would be no bus errors, and the DSA would blink it's green LED. What I deduced was going on is more or less chance;  there is a 10 millisecond interscan delay by default when you're using Polled I/O connections to your DeviceNet scanner.   Sometimes, the DSA was powering up and broadcasting it's DUP MAC ID CHECK message on the network during the interscan delay.   When it did, it didn't hear a response, and powered up at 250 kb and waited for a connection to be established. Sometimes, though, it would broadcast it's DUP MAC ID CHECK while other traffic was going on.   Because the bit widths are twice as long at 250 KB as at 500 kb, the messages were over-writing other traffic on the network, causing CAN frame errors.   These are the instances when the CAN error counters were jumping, and the Bus Off errors occuring.  It happened twice because the DeviceNet specification requires the DUP MAC ID check to be broadcast twice before a device can join the network. All I would have had was conjecture if the Netmeter hadn't been able to show me the CAN errors clearly.   The fix is just to be sure that the Autobaud feature is always turned on before you install a starter auxilary.

[Ken Roach 194]

Netmeter scores again ! One of my field service guys calls up working on a DeviceNet installation for which he's a little overwhelmed;  it uses a PLC, I/O, and cable.... none of which are made by our Company.   But we're the "DeviceNet Experts" so we got called out to fix the problem. After doing all he could checking voltages, using a scope, and fiddling with configuration tools he was unfamiliar with, he gave me a call. As mentioned before, our distributor just bought three of these as demos.  So this fellow rented the NetMeter from the distributor and applied it to this network. Surprisingly, he didn't find anything wrong.   Voltage drop, CAN errors, traffic... all clean. That is, I think, what the Netmeter is best at;  telling you that the system isn't physically malfunctioning so you don't spend you time with a scope and wire strippers when you need to be looking at traffic analysis and firmware.    Vice versa, it can help you stop wasting your time banging on software and PLCs when your problem is a loose wire or noisy power supply. I eventually identified the anomalous traffic coming from the master PLC and confusing the slave I/O modules, and forwarded that to the firmware developers for the Scanner. Now I'm sure that the distributor will want to SELL some of these, instead of loaning them out !

[93lt1 0]

I priced one of these through our local distributor, kinda pricey! How much was the list price where got yours??

[Ken Roach 194]

Ain't cheap.   Here they sell for $995. The other handheld meter I've found for DeviceNet, the DeviceNet Detective, sells for $1695. A-B sells their ControlNet signal meter for $450, but it only gives you LED readouts. A similar LED-only DeviceNet meter is available from Dearborn Group for about $300. That's why I wouldn't expect somebody with a small DeviceNet network to need or want one.   I think that big factories full of DNet, or factory guys (hint, hint) from DeviceNet manufacturers ought to have one.

[93lt1 0]

So my quote of $940 is actually pretty good?? Just figured I'd check!!