rotary encoder control & heater sequence,,,please help...SOS:(

to all PLCS gurus, pardon a question from a newbie..

1.) A conveyor will be controlled by a motor speed controller, to be specific a gear motor speed control & linked to the plc.. this motor is an ordinary motor only, with a rotary knob use to vary its speed.. as part of its system improvement,we will install an improvised rotary encoder (using a rotary plate with a number of punches & a photosensor).. how will i be able to control this rotary encoder on a ladder?

2.) I am tasked to modify a certain machine.. Part of the system sequence is the control of 3 heaters.. I have a SV set on the temperature controller, when my sensor "says" that there is no enough temperature 1 heater will turn on.. Agen, the sensor detects temperature, if still not enough my second set of heaters will turn on.. And agen, my sensor detects, if stil not enough, my last set of heater will turn on.. With this sequence, will my temperature controller be enough in controlling the system temperature without linking it to the PLC?

PLEASE HELP

#1) I am guessing that the speed is not very critical and not very fast based on the fact that you are using a photosensor as opposed to an actual encoder. That being said, here is a simple, but not super accurate way. Although it works well.

Speed is measured over time. You can not take a snap shot of the sensor status and tell the speed of anything.

Use a CTU (counter) and count the pulses from the photo-eye. Use a ONS (one-shot) so the counter only indexes one count per On/Off cycle.

Set a timer for 1 second. When the timer DN (done bit) comes on, trigger your speed calculation with the DN bit

Physically measure out how many pulses per meter of belt.

Now you know how many pulses there are in a meter and you know how many pulses you are getting per second. So you can easily compute your "meters per second".

The last rung, if the DN bit is ON, should RES (reset) the counter and restart the timer.

The speed output from this might jump around because of scan times, so to average it out you could increase the timer to read for 2 seconds and then divide the count by 2. Slower, but steadier.

#2) Not enough information provided to answer the question, but from what you explained, it seems like it should work.

thanks soo much , the star..you have confirmed something that was playing at the back of my mind..i will definitely put that into action..
regarding my 2nd question, am i correct in thinking that since a temperature controller is a stand alone system & does not need a PLC to fire a correct output, i do not need to insert to the ladder the modifications of the system instead, temperature controller configuration should work (though i am not very familiar with temperature control system)..i have a temperature controller capable of having three control outputs (heater to be specific), does these three output fires at the same time or 0ne at a time?..sory for asking you, maybe you knew better because even the tech support (here on our area) of the product could not confirm..i would greatly apreciate your attention upon my inquiries

Hard to tell without knowing your exact setup. Although, I would guess that the three outputs are designed for three seperate zones. Each heater controller independent of the other.

If you are heating one area or tank, then you would run them all off of the same thermocouple. This would mean that they all turn on at the same time.

I suppose you could use three seperate thermocouples and have different set points for each heater.

Example: If the desired temp was 210C then Heater 1 ON<210C, Heater 2 ON<205C, Heater 3 ON<200C.

This way all three would come ON to get up to temperature, Heater 1 would maintain, and Heater 2 could come ON during heavy loads.

oh, i see..each heater must have their own thermocouple, therefore i need a temperature controller that is capable of handling 3-in and 3-out @ the same time or a different temperature controllers for each set of heaters..but i dont think i can find a temperature controller having 3-in & 3-out or that is capable of controlling 3 different system at the same time..wheiw, this is harder than i thot..

I would say that if there is only one input, then they would all come on at the same time.

There are multiple outputs to divide the load of the heaters. For example, a 6000kw controller could have three 2000 watt heaters or two 3000 watt heaters connected to it.

Each manufacturer is different, so check the datasheets.

Switching 1,2 or 3 elements will be OK for very crude control however if you need accuracy the usual method of controlling an electric element is time duration. For a given period e.g. 10 seconds the heater is turned on for 2 off for 8 =20%, on for 3 off for 7=30% and so on.
The switching is normally done with a solid state contactor

pardon me roy of vancouver, i was reading ur reply but could not get a clear picture of it (sory, looks like my mind hangs up today)..can you please elaborate ..thanks