Internet PLC Forum

I'd like to point out your information is not clear as to what is happening now and what events happened when.

From what little I've been able to glean, it could be thermal shutdown of the 5 volt regulator.


Evan

If SMC don't want to do a swap you could turn it into a, kind of, three wire sensor by having a pulldown resistor than will reduce the low level to a lower value.


Evan

Just to address the OEM point, most machinery is OEM built and plenty have simple PLC programs running in them.  Some use locked programs some don't.  Some are very large and complicated machines and no one tries to fiddle with them while others are simple and obvious how they work.

The ones that have a simple function are the sort that TriPLC is most suited to and are also the ones that are sandwiched in the middle of bigger equipment acting as glue or atleast that's what the management are expecting to happen.  Being able to tweak such a device is a desirable abillity.

It's also common for these to be a one-off contract job that is slapped together and the "official support" soon fades away.  The software is not stored anywhere nor documented properly, relying on the ladder diagram to be the documentation.  Being able to edit the PLC contents directly is a very common situation, often having to later makeup the labelling for the I/O also.


Evan

http://www.tri-plc.com/yabbse/index.php?board=1;action=display;threadid=764

PID isn't that hard to roughly tune by hand, can get very tedious though.

The Proportional component should be a primary component and set first.  Keep increasing the strength of this until it causes oscillation then back off a whole third.

The Intergral component becomes important for temperature control to achieve zero error with a steady state setpoint.  This is ment to be a time factor of the oscillation period but problem is the heating and cooling is not usually even so this might take many days or even months of fine tune.  Normally only adjust this after Prop has been set.  In some PID functions this will drastically modify the Prop action.    Sorry I'm not much help in defining this more clearly.

Forget about the Derivative component for temperature control.


Evan

Single phase motors are best left alone.  Either add an external brake or replace the motor with a three phase one and use an inverter/vector drive to speed control it.

The PLC would be used to sequence both methods but is not the device that does the physical work - that would be either some contactors or the inverter.


Evan

Your final question is a valid concern.  Counters are a very demanding job without support harware and when the processor is doing many jobs it can't afford to spend too much time on the one function.

There is, however, more than one way to skin this cat.  Yes you can use a direct interrupt from the rising edge of each of the phases, which I assume is roughly how the basic method is done.  The enhanced method will likely use a timer based interrupt that observes all quadrature transistions and therefore could achieve the 4x resolution feature.  In both cases the IRQ should be a higher priority than the comms IRQ.

PS:  My musing are, on the most part, general knowledge.


Evan

Yep, those encoders look fine, you'll need to watch you don't go too fast though.  The T100MD is rated for 10kHz, normally this means the pulse rate of each channel so the max count rate is 40000 counts/s.  I'll take a stab and say that's optimal so you should stay well clear of it by limiting yourself to 5 kHz absolute max pulse frequency which for a 1024 line encoder is about 300 rpm (5000 Hz x 60 sec / 1024 lines = 293 rpm).  A good target for the encoder would be around 100 rpm.

Also use the command SETSYSTEM 4,1 to give proper counting on channel one - I'm not sure if this provides full resolution or not but this is not a concern for you as the resolution is already plenty high enough.

Use an aux contact of the M2 contactor as the supply for all other contactors and valves.  This then becomes your safety enable as well as powering the pump.  The coil of M2 is powered through a series of contacts:  SW1, SW2, PLC_OK, INVERTER_OK, M2_OVERLOAD,  M3_OVERLOAD, M4_OVERLOAD.

The PLC can turn the hydraulic pump on and off with the PLC_OK output.  All other outputs control individual items and all other limit-switches and push-buttons are individual PLC inputs.


Evan