Hello Guest it is January 29, 2020, 09:26:48 AM

Author Topic: pwm mode set up issues  (Read 7757 times)

0 Members and 1 Guest are viewing this topic.

pwm mode set up issues
« on: October 01, 2008, 11:11:25 PM »
Hello, I am new to Mach 3 and have a problem.  I am trying to use the pwm spindle output and something is not working properly.  I need to ultimately get a 0-10v signal to my motor drive, and have purchased a board from Baldor to do just this.  It accepts 4-20ma and outputs 0-10v.....their part number BC145.

I have set up the spindle config, assigned ports, etc. and I think that part is working.  I don't have a way to measure frequency so I'm just using a digital volt meter set on 20ma.  With this connected in parallel with one of the leads at it's attachment point on the converter board, I get a reading of .2 - .8.  Problem is I get no voltage output from the board.   I know it's not advised to check the pwm with a voltmeter, but it's all I've got at the moment and I'm trying to decide if I have some configuration issues in Mach3 or if maybe my board isn't working.....I just got it today from the manufacturer, but it could be defective.  Has anyone ever tried to measure this with a voltmeter and did they get similar values, or does it sound way off? 

My problem may well be in my configuration but I have tried various settings all day and have had no luck. ???

Thanks in advance for any suggestions, and if more information is needed to make more sense, please ask! ;D

Jeff
Re: pwm mode set up issues
« Reply #1 on: October 01, 2008, 11:52:52 PM »
Hi Jeff,

According to the manual, the Baldor BC145 is a signal isolator. It can accept a voltage input or a current input and produces an Isolated 0-10V output.

http://www.baldor.com/downloads/manuals/_downloads/1373-700.pdf

I don't see anywhere that says it accepts a pwm input. To do what you want you need some circuitry that converts the Mach PWM output to a 0-10V voltage or a 0-20mA signal, then feed that into the BC145. I don't believe that you can just feed the PWM signal from the parallel port directly into it. Depending on the load presented by the BC145, you may end up damaging the parallel port.

What you need is something like the DigiSpeed DC-03 or DC-06 I sell. The DC-03 converts the PWM signal to an isolated 0-10V output signal that can drive your motor controller. It would replace the BC145.
http://homanndesigns.com/store/index.php?main_page=product_info&cPath=1&products_id=21

The DC-06 does the same thing, but uses the step/dir output from Mach instead of the PWM signal.
http://homanndesigns.com/store/index.php?main_page=product_info&cPath=1&products_id=39

By the way, what DC motor controller are you using?

Cheers,

Peter.


----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com
Re: pwm mode set up issues
« Reply #2 on: October 02, 2008, 09:45:13 AM »
Hi Peter,

I really appreciate your help here!

I was thinking the pwm signal output from Mach3 was a 4-20ma signal.....I guess that was wrong? :-[  When purchasing the board, I just told them I needed one that received 4-20ma input as I thought that's what I had to work with.....so it's my fault for giving them the wrong info.

I am interested in your board.  Which of the two would you recommend, or will they both provide the same accuracy in my application?  I am using this on a mechanical fuel system flowbench I just built.  I want to create a sweep program that will bring pump speed up to 450rpm for a few seconds (this is where I will begin recording data), then sweep the rpm from 450 to 5000.  I will record the data from this sweep, thus giving me the info I need.   I am using Mach3 to allow me to control the rate of the sweep because at this point I don't know how fast it will need to be to give me the data file size I need.  I just need a board/software combination that will give me a smooth, variable 0-10v signal. 

I have a Baldor BC203 motor drive, and a 5hp Baldor motor p/n CD9105.  I have the drive operational in "manual" mode using a 10-turn pot, but want to be able to automate the sweep to provide repeatable test results.

Thanks for your help!!!!!

Jeff
« Last Edit: October 02, 2008, 04:40:51 PM by blownalcohol »
Re: pwm mode set up issues
« Reply #3 on: October 02, 2008, 04:37:37 PM »
Hi Jeff,

Sorry to hear yo had received bad advice. I'd recommentd the DC-06 with the optional DC/DC converter. The Converter removes the need for the Motor Controller from having to provide the supply voltage the DC-06. It mayalso give you a bit better linearity.

As with all my products if it doesn't do what you want, you can return it for a refund.

Cheers,

Peter.
----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com
Re: pwm mode set up issues
« Reply #4 on: October 02, 2008, 04:47:20 PM »
Peter,

I would like to get your opinion on something if I could.  I talked to the board manufacturer and it was suggested to place a resistor across the input terminals of the bc145 and change the jumper from current (where I had it) to volts.  Upon doing this I was able to generate 0-8.8v while reading the output with a voltmeter and changing spindle rpm in the software.  I hooked it up to the dc drive (bc203) and tried it.  The motor will turn, but it is pulsing.....slowly at low rpm and quickly at higher rpms.  I am wondering if the cycle from the pwm port is getting passed through the board since it's switched to volt input and not current.  What do you think?  I may just need to get another board, but naturally having paid over four times what your board costs I am trying to use what I have if possible. 

Thanks for your time,

Jeff
Re: pwm mode set up issues
« Reply #5 on: October 02, 2008, 07:01:01 PM »
Jeff,

Their may be some filtering somewhere in the isolation board that is working in your favour.  From what you are experiencing it appears that some filtering is occurring, but not enough, thus the pulsing.

Try this. Go into the spindle set-up tab in Mach3 and change the PWM frequency to 500Hz. If that doesn't smooth it out, increase it to 1000Hz. Let me know how you go.

There is a downside to increasing the PWM frequency though. As you increase it, you loose resolution (the number of voltage values you can generate).

THe number of volytage steps you can get out Mach is governed by;

Number of Voltage steps = Mach3 kernel speed/PWM frequency

If you are using a kernel speed of say 25KHz and you set the PWM frequency to 50, then you get 500 steps between 0V and your Maximum voltage(10V)


So if you increase the PWM frequency to 500, you will only have 50 steps. This may be fine for your application. To get better resolution, you can change your Mach3 kernel speed. Say from 25KHz  to 60KHz, or 100KHz assuming your PC is powerful enough.

Anyway let me know what you find.

Cheers,

Peter.
----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com
Re: pwm mode set up issues
« Reply #6 on: October 03, 2008, 11:46:27 PM »
Peter,

Just wanted to let you know I changed the frequency to 500 this morning just as you suggested and guess what.......it works!!!!  Thank you very much for taking the time to help me.
Jeff
Re: pwm mode set up issues
« Reply #7 on: October 04, 2008, 02:05:27 AM »
Peter,

Just wanted to let you know I changed the frequency to 500 this morning just as you suggested and guess what.......it works!!!!  Thank you very much for taking the time to help me.
Jeff

Hi Jeff,


I'm glad you were able to get it working. Especially without any additonal cost.

Cheers,

Peter.
----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com

Offline budman68

*
  • *
  •  2,360 2,360
    • View Profile
Re: pwm mode set up issues
« Reply #8 on: October 04, 2008, 08:22:48 AM »
Wish I had a 1/16th of the electronics intelligence, Peter has. :D

Nice job, Peter-

Dave
----------------------------------------------------------------------
Just because I'm a Global Moderator, don't assume that I know anything !

Dave->    ;)
Re: pwm mode set up issues
« Reply #9 on: October 04, 2008, 06:37:42 PM »
Hi Dave,

I appreciate your kind reply.

Cheers,

Peter.
----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com