Controlled motor start-up

I've got a Mitsu FX2N with which I need to start around 20 motors. Ideally I'd like to do this by having a delay of approx 1~2 seconds between each starting up. What would be the best way of achieving this? I was thinking along the lines of using a table/timer combination but I'm not 100% sure on how to do it.

Thanks
Dave

Dave,

Does your Mitsu instruction set have comparitave contacts? If so 1 timer will do.. The timer will be initated buy the start signal. Use the comparision to compaire the timer accumulator with constants to start the motors in sequence..

How about stepping a shift register? That is pretty easy although my recollection of the Mitsubishi A series is that it does not have a shift register, you have to use shift bit right and left.

tIMERRRRRRRRRR

You can do this like Mike has suggested with one timer. We do this on chippers. Something you need to consider is what happens when a motor trips out or is stopped for some reason. What about interlocks? Now you have a different scenario. It will work, but like everything else consider all the what ifssss. If you will make a list of these before you start programming it will save time in the long run. We actually startup in one sequence and shut down in reverse order. As BobB stated a bit shift would work also.
Good Luck

Wish he was using a 9030, I'd recommend a "Drum" sequence program.

Does Mitsi have the capability?

regards.....casey

Wish he was using a 9030, I'd recommend a "Drum" sequence program. Does Mitsi have the capability?

Click to expand...

Not the last ones I used. They did not even have a shift register. You had to roll you own with bit shift.

A drum sequence function is only like a circular shift register anyway. It is pretty easy to program shift left/shift right anyway.

ok...

Why not use a timer that increments a counter?

1: The delay between start can be adjusted by adjusting the timer value, ( or the current counter value)

2: As mentioned, increment a counter value every time the timer "times" out. For a larger motor, have longer delays between motors starting.

If one needs to include interlocks, it's simple. Just don't allow the counter to increment anymore if an interlock problem occurs.

I have used this method plenty times before and find it to be quite reliable and dynamic.

Waynes,
i cant reach your words, would you explain it more detail?
curious...

thanks,
reza.

Waynes,
i cant reach your words, would you explain it more detail?
curious...

Click to expand...

Using a counter is similar to using a shift register. You can use timers of different length to either increment the counter or move the shift register. The only real difference with the output is that with the shift register you already have a bit to turn on the output. With the counter a series of compares are used to generate the output bit.

Dave,

I like ElevMike's method the best. I use it a lot. Using the RSLogix LIMIT command, the auto-start timer works just like a momentary Start pushbutton. Here is an example:

I like ElevMike's method the best. I use it a lot.

Click to expand...

Relative. Many PLCs have a limit command. They all work differently.

The methods mentioned here are all workable. A lot depends on the programmer, his/hers likes dislikes etc.

I use shift registers extensively because they are very easy to implement in Omron PLCs. I also use reversible shift registers for load control. Marvellous things. Many PLCs do not have them.

Generally do not use limit. It is too limiting. Use ZCP or ZCPL (long) instead. 2 outputs, one below the lower set point and 1 above the upper set point. Lower turns on, add some load, upper turns on, drop some load. Very powerfull with the reversible shift register. Great differential control.

Lancie, one of the great things about PLCs is that we all find different ways of doing things in different PLCs. The way we do it may be different but the result is usually the same. The net result is that the thing works and the customer is happy so WE GET PAID!!

At the end of the day that is all that matters, apart from our egos. Hopefully the customer comes back, because he is happy, and gives us some more work, hopefully at a better hourly rate.

Bob,
I am afraid tahat you lost me here.

Use ZCP or ZCPL (long) instead. 2 outputs, one below the lower set point and 1 above the upper set point. Lower turns on, add some load, upper turns on, drop some load.

Click to expand...

What set points are you referring to? I thought the subject was how to start up 20 motors in sequence, with each motor start being separated by some time period. This is often needed where the electrical system does not have enough power to start everything at once, plus it just makes good sense in a process plant to start motors sequentially.

This can be done with two COMPARE functions, like "If START_TIMER > 20 and START_TIMER < 23, Then Energize Motor 3", or like my example, with one LIMIT function for each motor. With this method, it is very easy to change the start order of the motors, and the time until the next motor starts. How is that a more limiting factor than using a Bit-Shift routine? I find it much easier to make adjustment to the LIMIT command than to a Bit-Shift register. So what is the setpoint that you are talking about? What does it set, and how is it relevant to this topic?

Lancie, I think we are having the usual problem with different PLCs having the same instruction name but the instructions are entirely different.

This is what I was referring to and there are set points.

LMT(680) - Limit Control


Variations:

Differentiate Up

See Variations for more information.

Purpose:

When the execution condition is OFF, LMT(680) is not executed. When the execution condition is ON, LMT(680) controls output data according to whether or not the specified input data (signed 16-bit binary) is within the upper and lower limits. The contents of words C and C+1 are as follows:

C

Lower limit data (minimum output data)

C+1

Upper limit data (maximum output data)



If the input data (S) is less than the lower limit (C), the lower limit data will be output to D and the Less Than Flag will turn ON.

If the input data (S) is greater than the upper limit (C+1), the upper limit data will be output to D and the Greater Than Flag will turn ON.

If the input data (S) is greater than or equal to the lower limit (C) and less than or equal to the upper limit (C+1), the input data will be output to D.

The lower limit (C) must be less than or equal to the upper limit (C+1).

Click to expand...

I have used Waynes method with interlocks. I like it. It is simple to understand. I do like the shift register idea as well and may try that out too.

David