ladder logic: how 2 ramp up motor speed?

Any smart PLC people out there???
Could anyone send me (please!)
the ladder logic instruction on how to ramp up a motor?
not for hookup, simulation only...

Needs 2 speeds: 50% speed for 1st 20 seconds
then 100% speed for next 30 seconds
then shuts off.
Speed is displayed in a register (for later BCD display in 40001)
Motor is actually just a light. (00001 for example)

thanks, will really appreciate your input.

( email is: [email protected] )

Your question is wide open.

You usually do not "ramp up a motor" with a plc, most of the time we network from a plc to a drive or something that controls the motor.

Do a search for "analog".

Assuming u have a 2 speed motor all u need is a timer and 2 contacters. If u feel the need to involve PLC u dont need the timer anymore because PLC has one (many) also u can display the speed and a lot more fancy things.

My internet access is limited now hopefully i can post smth on weekend. Feel free to post more details.

Eugen

Nice Question

You can rump up motor speed only when you have analog ouyput and speed controller.
The general idea is to increment bit to the output register every certain time.
For example,your analog output is 12 bit=4096 you want 50% in 20 sec
To make it easy let say 50%=2000 bit
Run timer who give you pulse evry 1 sec each timer pulse increment 100 bit, in that way you will get 2000 bit in 20 sec.
you can run your timer each 0.1 sec and increment 10 bit.(that will give you better resolution).
Comper your output to 2000 when it equal or above, stop the timer.
By changing the timer and the adding number you can get what you want.
Some PLCs have build in function like that.check your PLC instructions set .
you can do it very esay buy your self.

Goog Luck

ArikBY's right if your doing a "ramp" from the plc you'll typically use an analog output. If you really want to get fancy you can use a quadratic equation to create a parabola, (Y = speed, and X = time on your cartisen plane). In the elevator application this is what we do (before digital drives came along) to provide a nice acceleration and decel ramp. If you want to use a stright ramp, just add a value to your output register every so many ms or so until you reach the desired value. You failed to say what PLC you might be using so if your looking for code youll have to specify the plc.

You can rump up motor speed only when you have analog ouyput and speed controller
or
Assuming u have a 2 speed motor all u need is a timer and 2 contacters
or
u can do it through PID controller in PLC or use Vector Control Method.
wel its not bed idea to ramp up the speed of motor and control it through PLC wel i belive u must go to have to Timer logic as the 1st timer should be On delay time and 2nd shuld be on dealy too
in case of PID u can verify the speed of motor through reference but not in case of timer
if i m worng plz correct me
thanks
Muhammad Faisal Qureshi

Hi Guys,
While nowhere near the expert level, I remember seeing the PWM function in AB for the MicroLogix 1500. So now I can ask a question that goes along the same line of the motor speed control. Briefly, how does the PWM function work in AB? Is it stand alone or for interfacing into a servo drive? Any thing to un-muddy the water?
Thanks.

Waggs


Due to economic conditions, the light at the end of the tunnel has been turned off.

Apparently nobody uses this feature much anymore, but most VFDs have discrete inputs that allow you to establish pre-set speeds for the VFD to operate at when they are turned on. This is a fairly easy way to accomplish the objective if you have a PLC without analog outputs. Then the programming is straightforward - you just need some timers and some holding contacts.

Just to add to what Tom said some VFDs have the ability to get what we call "pules train input" I never use it with ML but with PWM fun you can determinate ACC/DCC and frequency(work great with step motors) or only frequency. if you need one analog output you can use it with pules to analog converter (Red-Lion have it)very cheap and helpful.
BTW it work in the opposite way if you have HSC build in your PLC you
can use converter Analog to Pules.

Sounds like a student question to me...

Do you have any problem with that?
This site is for them too.

Keep in mind that PWM (pulse width modulation) and pulse train are two different animals. PWM changes the duty cycle of fixed frequency pulses to communicate a relative level. Pulse train changes the frequency of fixed duty cycle pulses to communicate a relative level. OK, I should ammend that. Some pulse train outputs do not maintain a fixed duty cycle. They have a fixed on pulse width equal to about half of the on pulse time at max frequency. But I digress.

PWM: Variable pulse width communicates level
Pulse train: Variable frequency communicates level

So a PWM signal will not correctly drive a pulse train input

Keith

Keith

Thanks for your exlenation that something I would not able to write
with my poor English.
I agree with that is two different things I mention them in same breath to show the use of pulse fun.

The DustMan,

Now back to your original question:

Needs 2 speeds: 50% speed for 1st 20 seconds
then 100% speed for next 30 seconds
then shuts off.
Speed is displayed in a register (for later BCD display in 40001)
Motor is actually just a light. (00001 for example)


SOLUTION:

Think about your OUTPUTS. You need at least one ON/OFF output for your motor. You also need two speed OUTPUTS, 1 for 50% Speed, and 1 for 100% Speed. You could use outputs Y1 and Y2 for these. You need an output for your analog speed value. In you case for training purposes this can be a memory register, say V40001).

1. Add a rung for your motor output, using the first available PLC output (Y0?). Add comments and symbols to tell YOU what it does. Add rungs for the two speed outputs Y1 and Y2, and document each one.

2. Add Inputs to turn the outputs OFF.

3. Add Inputs to turn the outputs ON.

For Steps 2 and 3, I would add a Timer, say T0, in parallel with the motor output. Start the timer when your motor Start switch is pushed. Set the Timer Preset Time to 50 seconds. Use comparison instruction inputs on each of the two speed output rungs: If T0 <= 20 seconds, then turn on Output Y1. If T0 > 20, then turn on Output Y2. If T0 = 50, (or just an XIO contact that looks at T0=ON), then turn off the motor. The timer accumulated value will reset to 0 if you put the timer in parallel with the motor.

Add two rungs that output your speeds to register V400001. If Y1 is ON, then LOAD (LD K50) the constant K50 and OUTput it to location V40001 (OUT V40001). If Y2 is ON, then LOAD the constant K100 and OUT to location V40001. Each of these two rungs should have 1 input and two outputs in parallel, a LD instruction and an OUT instruction.

This must be a student question.

It seems to me that Dustman is asking for how to change between two states, not on how to ramp up or control a motor. I dont want to tell Dustman how he does that, if he cannot figure that out himself he should start on another course !
(But Lancie1 does provide an allmost complete example on how to do it).