PWM confusion

mcham

mcham
Hi,

I am confused about the documentation regarding PWM. It appears that if I select PWM I get no spindle direction signals. Is this so?

In my world, it seems we should have one or both of the following:

A signal which indicates speed (your choice of PWM or analog). A signal that indicates CW or CCW (direction signal). Spindle off is indicated by an indication of zero speed.

OR

A signal which indicates speed (your choice of PWM or analog). A signal that indicates CW as well as another signal that indicates CCW. If neither is active, then the spindle is off

The documents might indicate two separate PWMs, one for CW and another for CCW. Does a machine that accepts this really exist?

thanks
 

tayloredtech

TayloredTech
Here's an example wiring.
 

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mcham

mcham
That seems fine if you do not use PWM. But look at what the docs say related to PWM. It seems that we have multiple PWM signals and no direction signals.
 

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tayloredtech

TayloredTech
I would possibly say that they would be a 0/100% PWM signal so in reality, just a 0v/5V signal maybe. Have you got a multimeter handy? If I'm right you could use a TTL style relay. @masso-support Do you clarification on this please?
 

masso-support

MASSO Support
Staff member
Hi mcham & Mitch

The Opto couple outputs work the same as they do when you use the Analogue output.

Pins 4 & 5 conduct when the spindle is turned on clockwise to start the spindle

Pins 6 & 7 conduct when the spindle is turned on in the Counter clockwise direction to start the spindle

Unlike the Analogue speed control the PWM output is split over 2 outputs. Pin 2 outputs TTL PWM 0 / 5 volt when you select clockwise and pin 3 outputs TTL PWM 0 / 5 volt when you select counter clockwise. Since these signals are for speed rather than on/ off operation using a TTL relay will not work.

Something to be aware of is the PWM signal is 4khz minimum which may be a problem for your VFD if it cannot accept a signal that high.

What VFD are you using that requires PWM?

Cheers

Peter
 

mcham

mcham
I am using a CNC4PC CS41S to convert PWM to ISOLATED 0-5V analog for a PM25MV mill. I have the CW speed working fine. It now appears that this split PWM makes it so I cannot make direction work. The C41S requires a single PWM(ttl) and a DIR(ttl) signal. I would be surprised if any PWM application would require a split as is provided.

thanks for the responses!
 

masso-support

MASSO Support
Staff member
Thanks mcham.

I see your problem. Have you thought about using the Analogue setup rather than the PWM to drive your VFD.

The first issue of the 0-5 volts you need can be solved using a simple voltage divider circuit to half the voltage from 0-10v down to 0-5 volts.

Basically a voltage divider is made from 2 resistors and the output is proportional to the ratio of the resistors. see the circuit below.

The 2nd circuit is basically the same thing but using a 5K variable resistor for fine adjustment. I would use a 10 turn or 25 turn pot for the Variable resistor and that will give you get very fine adjustment but any 5K Variable resistor would do. Just try and use a linear one rather than logarithmic as the latter is much harder to adjust.

Actual values are not overly critical but it is a very simple and effective circuit. Set the output of Masso to full speed, 10V out, and adjust the pot to give 5 volts. Then connect the VFD and readjust if necessary. The VFD may cause the output voltage to drop a little because of the load.

The 2nd problem of the TTL solves itself because pins 2 and 3 output TTL 5 volt on and 0 volt off when in Analogue mode .

Alternatively you can use the opto couple outputs 4, 5, 6 and 7 instead and supply them with a 5 volt supply with it's ground referenced to your VFD. That way they will behave like TTL but you have the security of the opto isolation. Your VFD may already supply 5 volts to use with a relay so it may be even easier to do.

Hope that helps

Cheers

Peter

PS I personally haven't come across a VFD that uses dual PWM signals. (not yet)
 

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tayloredtech

TayloredTech
What Peter said, was thinking it. Just no idea how you'd make it haha. Thanks Pete, that's going to help me in so many ways for other projects. Legend.

Mitch
 

tayloredtech

TayloredTech
Quote from MASSO Support on June 7, 2019, 11:29 am

The 2nd problem of the TTL solves itself because pins 2 and 3 output TTL 5 volt on and 0 volt off when in Analogue mode .

Alternatively you can use the opto couple outputs 4, 5, 6 and 7 instead and supply them with a 5 volt supply with it's ground referenced to your VFD. That way they will behave like TTL but you have the security of the opto isolation. Your VFD may already supply 5 volts to use with a relay so it may be even easier to do.

Hope that helps

Cheers

Peter

PS I personally haven't come across a VFD that uses dual PWM signals. (not yet)

Is that bottom rail a ground?
 

mcham

mcham
Peter,

If I go to o-10v I still need to opto isolate the analog signal. So, if I have to give up the CNC4PC C41S, can anyone recommend an isolator that will isolate the analog signal?
 

clover

clover
@mcham
can anyone recommend an isolator that will isolate the analog signal?

Opto isolators are generally non-linear devices. In other words current in does not necessarily accurately track current out (they are current operated devices). Analog or near linear opto isolators do exist but they need additional circuitry to operate and do not just drop-in as with conventional optos.

Unfortunately I cannot find a commercial ready to go unit that will convert 0-10v input to 0-10v isolated out. If you have electronic experience it would not be too difficult to knock-up a unit and in this case I refer you to this data sheet. In particular to page 13, figures 16 & 17 (These are basic circuits and their operation at or near zero voltage will need to be proved). Patrick
 

masso-support

MASSO Support
Staff member
Hi mcham

Whie it is possible to optically isolate a DC signal, finding an off the shelf board to do it is another matter.

As an out of the box idea have you considered an analogue to PWM converter and then feed that into your optically isolated PWM to Analogue converter. It's an extra step but should work.

I found this board to take the 10V from Masso and convert it to PWM. It is based on the NE555 so the frequency shouldn't be too high though they don't mention what it is. They also don't mention what the POT is for but seeing that it connected to the input voltage I assume is to fine tune the PWM duty cycle.

https://www.banggood.com/Voltage-To...-p-1183840.html?rmmds=search&cur_warehouse=CN

If I think of anything else I will let you know.

Cheers

Peter
 

masso-support

MASSO Support
Staff member
Quote from TayloredTech on June 7, 2019, 11:47 am

Quote from MASSO Support on June 7, 2019, 11:29 am

The 2nd problem of the TTL solves itself because pins 2 and 3 output TTL 5 volt on and 0 volt off when in Analogue mode .

Alternatively you can use the opto couple outputs 4, 5, 6 and 7 instead and supply them with a 5 volt supply with it's ground referenced to your VFD. That way they will behave like TTL but you have the security of the opto isolation. Your VFD may already supply 5 volts to use with a relay so it may be even easier to do.

Hope that helps

Cheers

Peter

PS I personally haven't come across a VFD that uses dual PWM signals. (not yet)

Is that bottom rail a ground?

Yes it is. I have updated the drawing to show this.

Cheers

Peter
 

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