OK, I will be more blunt.
kamenges said:
You shouldn't infer, Peter. I'm pretty sure mcafone doesn't know.
What you need is:
1. Is a very fast sample time. The faster the better. 0.5 milliseconds is easy.
What you need is to record the maximum pressure your test gets to. The pressure will build and when the item ruptures the pressure will quickly drop. If the pressure readings can be logged every 0.5 millisecond then it should be easy to find the peak pressure.
2. The analog response should be fast, much faster than PLC analog reading. PLC analog inputs are good for slower temperature controls. Our controller does an 8 times over sampling. That means we do 8 A to D conversions every 0.5 milliseconds. That is 62.5 microseconds per sample. We then average the 8 analog. This effectively extends the resolution by the sqrt(8) bits. It also means the all the averaging is done within the sample time, not over multiples sample times which would cause phase delay.
3. High resolution. We have a 16 bit A to D converter. This allows us 0-32767 counts in uni-polar mode or -32767 to +32767 in bipolar mode. One must use wiring tricks to bias the system in bi-polar mode so I will assume the uni-polar mode is used.
Now for the calculations:
Given the pressure range is 0 to 10000 psi
(10000 psi/32767 counts)*(1 count/0.5 millisecond)=610 psi/second.
What this means is that at 1 count per 0.5 milliseconds the minimum detectable rate is 610 psi per second. One can try increasing the pressure at slower rates but that would mean the controller would not see a change in counts each scan. This is just wasted time. The situation for the slow PLCs is much worse. I know you can miss a whole pressure transient with the scan of a PLC.
Conclusion.
1 The real resolution is 10000/32767 or about 1/3 psi per count.
Not the 1/20 psi I mentioned before.
2. A PID is not required. What would the set point be? You don't know the pressure where the parts will fail. Just use an open loop control output so the pressure increases somewhere around 600 psi/second and then wait for the pressure to drop. The pressure drop occurs when the item bursts or fails. It is easy to test whether the new pressure is less than the previous pressure. This can be done every 0.5 milliseconds.
3. The peak value is the burst pressure.
4. Upload the graph of the test data and save it on the disk. Do this using Ethernet.
The RMC70 can do all of this easily because is was designed to do hydraulic position/pressure/force control. No PLC required.