Looking to add an upper and lower limit switch to this control box.
System runs a cogged belt up and down a track.
I have a 3p motor control by a vfd
Wireless controls(momentary) into the x terminals on the vfd(3wire control)

I need to add two limit switches but they need to sequence. After tripping the limit, it decelerates and then passes back past the switch.
I’m thinking of using latching relays in between the wireless and the vfd

 

Hello, this thing on?

 

Looking to add an upper and lower limit switch to this control box.
System runs a cogged belt up and down a track.
I have a 3p motor control by a vfd
Wireless controls(momentary) into the x terminals on the vfd(3wire control)

I need to add two limit switches but they need to sequence. After tripping the limit, it decelerates and then passes back past the switch.
I’m thinking of using latching relays in between the wireless and the vfd

Can you show us a wiring diagram of your system? It would help us to understand what you have and how to modify it.

 

Can you show us a wiring diagram of your system? It would help us to understand what you have and how to modify it.

 

From what I can read of your very poor pictures it looks like you have a Siemens Logo 24RCE controlling the VFD. Is it not possible to reprogram the Logo 24RCE to do what you want. Is the VFD already programmed to ramp up on start and ramp down on stop ?

Les.

 

Can you post it in black and white? also the Logo outputs are not shown, usually any changes are easiest in the Logo, as Les mentioned.
Do you have the logo logic program?
Max.

 

Some drive packages include limit switch inputs to do just exactly what you describe, while others do not support that function. You will need to consult the instructions for that drive to see if it can even work that way. I see that one post claims that function is not available with the drive that you have. In that case you may be out of luck. BUT you need to read and understand the manual for the drive.

 

Some drive packages include limit switch inputs to do just exactly what you describe, while others do not support that function. You will need to consult the instructions for that drive to see if it can even work that way. I see that one post claims that function is not available with the drive that you have. In that case you may be out of luck. BUT you need to read and understand the manual for the drive.

Yeah, same as above. Some VFDs have a bunch of inputs that you can use. So. Crank open the VFD manual and start reading.

 

That Lenze version appears fairly limited as to control inputs, not that many options.
Max.

 

I do not even see much of a speed control input, so it is not likely that ramping the speed down at some point is even possible. That is one reason that I have avoided the Siemens brand of equipment. If there is a directional control line and an analog speed control input then you could have either a simple RC ramp circuit handle the slowing at the end of a move or use a PLC with an analog output to generate the changing speed command. Once again, first study the manual to see what control functions are available.

 

So I’m really just trying to get away from the plc. I am trying to use a relay option to sequence the up and down limit switches. The prints show the original control boxes. They are expensive and overkill for my service crews to use. The cheap vfd shown in the first photo is set for 3 wire input and has all the need acceleration/deceleration functions needed. I am just trying to add an up and down limit switch inline with the controls.

 

So are you saying that there will be no PLC involved in the new version. Am I correct about this ?
What I THINK you are saying that you want is to drive the forward input to the VFD (The VFD being configured to ramp up when a forward or reverse signal is applied and ramp down when it is removed.) When the forward limit switch is reached remove the forward drive signal. Delay for a time to allow the motor to stop. At the end of the delay drive the reverse input to the VFD. Then do the same sort of thing when the reverse limit is reached as was done with the forward limit. You would need to tell us how you want it to behave when power is first applied.

Les.

 

OK, does that VFD have direction switches? or is the direction controlled by the polarity of the speed command voltage? And just how accurate does the position have to be that it reaches at each end of the move? I just had an inspiration for a control scheme that could be very simple and cheap, but not perfectly precise.

 

Yes I’d like to remove the plc

The vfd I’m using has x functions for a 3wire control(momentary push buttons for stop, up, and down) I’m using this setup now.
The

 

The machines i build, have a carriage the gets raised and lowered using a cog belt. I have an upper and lower limit switch that works by a flag mounted to the belt. The issue is that after the flag trips the limit switch switch go then goes past that trip point during deceleration. Once it changes direction it passes by and retrips the switch. So I need to them To deactivate depending on if it’s running up or down.
I wanted to use a series of latching relays to sequence the limit switch’s depending on the direction of the carriage

 

There is no metering, I set the distance traveled after the limit trip with the deceleration function on the vfd

 

What about using dynamic braking on the motor? Permanent magnet type? If so then consider the possibility of dead stopping the motor using magnetic braking (dynamic).

 

Can your VFD be configured so that it needs a permanent signal (Rather than a pulse to start.) for forward an reverse ? (The stop function would then be redundant.) If it could be configured that way then the UP limit switch would only cause the up direction latching circuit to trip off. And the same sort of thing with the down direction.

Edit. Another idea. If you made the limit switches like a toggle on/of switch so that when the flag on the belt passed it in one direction it would switch it on but in the other direction it switched it off then you could use the off to on transition to generate a stop pulse but ignore the on to off transition. This would probably require you to make some kind of springy tripping system for the switches.

Les.

 

No, and I’d like to keep it separate from the vfd. In case I have to use a different one down the line.

 

I was hoping to use the pulse from up