Ultra High Speed PLC with Analog input

I am searching for the fastest possible way to analyse an analog signal with an output frequency of 450Hz. I need to evaluate the slope and give a discrete output if the slope of the analog signal is in a specific range.

Is there a PLC which can do the above without missing any data due to scan times?
Is there an alternative analog signal analyzer which can do it and give discrete output that would stay on long enough for a slower PLC to see?

If it is a change in frequency that you are wanting to monitoring, then does a high speed counter achieve what you would require. ?

What slope or frequency would be considered out of range. ?

What brand of PLC do you currently use at your site. ?

I think this is too fast of an application for most PLCs. To get any meaningful information you would have to sample at least one tenth the period or about .22 milliseconds. You need multiple samples on each quarter cycle to view the slope.

Peter may come in on this.

Have you checked out National Instruments? They make LabWiew and also incredible fast harware PLCs and IOs.
I have heard that their standard equipment is used for motor control purposes (and the ignition timing must be accurate).

They hide here:
http://www.ni.com/products


Regards
Kalle

Gil47 said:

If it is a change in frequency that you are wanting to monitoring, then does a high speed counter achieve what you would require. ?

What slope or frequency would be considered out of range. ?

What brand of PLC do you currently use at your site. ?

Click to expand...

thanks for all of the responses... to clarify im not reading a frequency. I'm reading a 4-20mA signal which refreshes 450 times per second. I want a discrete output when the signal drops steeply... meaning it drops 3mA over 2ms. But if it drops 6mA i need to alarm etc.

I will check national instruments... Any other suggestions would be helpful.

use hardware:
one OPAMP and a capacitor will do this trick and some resistors.
make a differntiator of it.

With S7-300, the high-speed analog input module 6ES7331-7HF01-0AB0 can update its channels every 0.42 ms.
You could read the analog input every 1 ms by means of a cyclic interrupt and OB35.

I think that Beckhoff also have some fast analog inputs.

Is this maybe for a surge detection on a compressor ?

May be this is a possible option:
VIPA 331-7AF70(SM 331S - FAST Analog input - SPEED-Bus)
http://www.vipa.de/en/products/system-300s/signal-modules-analog/

I'm on a project with a similar high speed analog input requirement. I've had good luck with the Panasonic FP-X micro PLC. Scan time is <1 ms for a small program and they claim the update rate for the AFPX-AD2 analog expansion is 1 ms per channel. I'm an Allen-Bradley man myself, but I have to admit the FPWIN PRO software isn't half bad.

http://pewa.panasonic.com/acsd/plc/fpx/

I like the idea of the op-amp used as a differentiator with a peak hold second stage. Otherwise you need to digital sample at about 10 times the frequency to get a good slope depending on the nature of the signal.

Is there a PLC which can do the above without missing any data due to scan times?

Click to expand...

I doubt a PLC can do this without some sort of hardware assist. PLCs will have significant sample jitter at the higher frequencies.

A high speed input may do if the signal is a sine wave and can count the time between zero crossings or the time between peaks. The derivative is then
rate=amp*2*pi*hz or
rate=amp*2*pi/period

JesperMP said:

Is this maybe for a surge detection on a compressor ?

Click to expand...

This is for detecting a very small hole in fast moving pipe using a laser sensor with an analog output. the hole cannot be too deep.

I don't think you're going to find a plc that will do this. Maybe the National Instruments syuff mentioned before. I have heard they can do some pretty high speed stuff. A better bet is probably to PM Peter Nachtwey and see if he can set you up.

But now I'm curious. Why is the slope important for what you are doing? You seem to infer that a small diameter, shallow depth hole with square sides (almost infinite slope) is worse than a 150mm long gouge that come within 0.5mm of punching all the way through the wall (very shallow slope).

Keith

kamenges said:

I don't think you're going to find a plc that will do this. Maybe the National Instruments syuff mentioned before. I have heard they can do some pretty high speed stuff. A better bet is probably to PM Peter Nachtwey and see if he can set you up.

But now I'm curious. Why is the slope important for what you are doing? You seem to infer that a small diameter, shallow depth hole with square sides (almost infinite slope) is worse than a 150mm long gouge that come within 0.5mm of punching all the way through the wall (very shallow slope).

Keith

Click to expand...

The round hole is 2-3mm in diameter and is drilled into 60-90m/min multilayer pipe and must only puncture the top layer. It must be 2-3mm deep. if it is 10mm deep then i want to sound an alarm. But for robustness when using different pipe diameters rather than use the actual distances I want to only look at slope. That way I don't need any adjustment if I am looking at 32mm diameter pipe or 20mm diameter pipe.

OK, I think I understand now. I (incorrectly) assumed you were looking for random defects. But you are looking for a manufacturing error in a recurring feature.

While this is still a high speed application I don't think you need the processing power we thought you did. I don't think you need to do waveform analysis on this. A per-scan delta may be enough. Since this is a drilled hole the edges should be pretty square. So on the scan you go from the pipe into the hole you should see the complete depth change in one step. The worst case would be you are transitioning into the hole on a scan and you may have a partial delta. So you may want to look at the delta across any two scans to determine actual depth.

Part of the trick will be keeping your scan area stable. If your example is accurate and 3mm is good but 10mm is bad it may not be a big deal. But is 3mm is good and 4 mm is bad it doesn't take much motion to get outside your error budget.

Keith

I think the attached drawing is what an OPAMP would do to my analog input. This seems like it would greatly help analyse the signal. I've PM'd Peter for further help. Thanks everyone so much for all of your suggestions. I'm in contact with NI as well.