RPM from VFD to TouchDRO?

[Backporch]

I don't intend to change any gearing. Speed changes would be accomplished solely by the VFD.

Without going into gory detail, be aware that without using gearing to reduce the spindle speed (range), the torque at low speeds will likely not be to your liking.

Gearing both reduces speed and increases torque. I think most would use the vfd frequency to fine adjust the spindle speed within an appropriate gear range.

Also some VFDs do strange things at low speeds if the spindle is lightly loaded and there is significant backlash in the gear chain.

 

[Greyhound]

Without going into gory detail, be aware that without using gearing to reduce the spindle speed (range), the torque at low speeds will likely not be to your liking.

Gearing both reduces speed and increases torque. I think most would use the vfd frequency to fine adjust the spindle speed within an appropriate gear range.

Also some VFDs do strange things at low speeds if the spindle is lightly loaded and there is significant backlash in the gear chain.

Absolutely, I've considered that. My motor is dual speed and I've chosen to run the lower speed (1720) delta configuration for that very reason.

 

[B2]

At the your first posting you did not mention a mill . I was thinking lathe. It is certainly easier to install a hall sensor on most lathes than on a mill. Which mill do you have? Motor size? Which VFD size. I quickly looked at the manual for the TECO E510 series. It does not seem to have a simple digital output but does seem to have a serial data output per @den-den comment above. I have never looked into this so do not really know what this involves.

One of a couple of brute force approaches toward this is to wind a wire a few turns around one of the 220 lines going from the VFD to the motor. This would then be connected to a signal transformer and then the secondary of the transformer might be be to condition to provide the digital signal. OR the power wire is run through magnetic core and turns of wire are also wound on the core to provide the secondary. It might take a little bit of electronics to do the conditioning of the signal. The beauty of this is that it comes right off of the power to the motor and because of the transformer it is essentially electrically isolated from the 220V. The not so beautiful aspect of it is that it is inductive. As such the coupling in this transformer is frequency dependent and the voltage out might be low at low frequencies. However, most motors do not want to run at low frequencies anyway.

I will think about this some more. Meanwhile you should look at the possibility of putting a hall sensor somewhere near the spindle. An RPM reading is much nicer to have. The VFD will probably provide the frequency directly on its display, but only when the power is available to the motor.

One of the reasons I like having the approximately correlated 0-10 voltage INPUT reading to indicate the VFD frequency is that it is available before the motor is actually turned on! I am not for sure if the VFD Output 1-10 volt signal is available prior to the the motor being turned on.

 

[Greyhound]

At the your first posting you did not mention a mill . I was thinking lathe. It is certainly easier to install a hall sensor on most lathes than on a mill. Which mill do you have? Motor size? Which VFD size. I quickly looked at the manual for the TECO E510 series. It does not seem to have a simple digital output but does seem to have a serial data output per @den-den comment above. I have never looked into this so do not really know what this involves.

One of a couple of brute force approaches toward this is to wind a wire a few turns around one of the 220 lines going from the VFD to the motor. This would then be connected to a signal transformer and then the secondary of the transformer might be be to condition to provide the digital signal. OR the power wire is run through magnetic core and turns of wire are also wound on the core to provide the secondary. It might take a little bit of electronics to do the conditioning of the signal. The beauty of this is that it comes right off of the power to the motor and because of the transformer it is essentially electrically isolated from the 220V. The not so beautiful aspect of it is that it is inductive. As such the coupling in this transformer is frequency dependent and the voltage out might be low at low frequencies. However, most motors do not want to run at low frequencies anyway.

I will think about this some more. Meanwhile you should look at the possibility of putting a hall sensor somewhere near the spindle. An RPM reading is much nicer to have. The VFD will probably provide the frequency directly on its display, but only when the power is available to the motor.

One of the reasons I like having the approximately correlated 0-10 voltage INPUT reading to indicate the VFD frequency is that it is available before the motor is actually turned on! I am not for sure if the VFD Output 1-10 volt signal is available prior to the the motor being turned on.

Mill is an Enco 100-1598…basically a BP clone. It has a 2HP motor and I’m using a 3HP TECO E510 drive.

 

[mksj]

The 0-10V analog output is always on, it reads 0 on the RPM meter and tracks all the way down to the minimum RPM of 40 RPM to 4500 RPM on my mill. If one is running in SLV then the actual RPM displayed is accurate it is not running in V/Hz where there is no feedback adjustment for slip. The E510 does not have a pulse output function, the other option is just have a simple scalable voltmeter display and scale it to display the output as RPM.

Hall sensor is usually a straight forward install, in particular on a single or dual speed application, if there is a back gear then you need a switch to adjust the range. I have also placed a hall sensor and magnet ring on the bottom of the mill ram/spindle in combination with a ring LED light.

Back gear sensors, upper switch goes to the tachometer display.

 

[B2]

The 0-10V analog output is always on, it reads 0 on the RPM meter and tracks all the way down to the minimum RPM of 40 RPM to 4500 RPM on my mill.

That is nice! I would have connected the output voltage on my lathe, but I would have had to run another wire to the front panel meter. I so I just took the voltage off of the speed control pot. It is not very accurate, but it is fine for what I want it to do and I do get the value before turning on the lathe. Once the lathe is on I can just look at the VFD display for the frequency.

By the way, from @Greyhound 's first post he did not want to add another meter. He wanted a digital signal to feed to his TouchDRO. so that he could just use it's display.

 

[Greyhound]

The 0-10V analog output is always on, it reads 0 on the RPM meter and tracks all the way down to the minimum RPM of 40 RPM to 4500 RPM on my mill. If one is running in SLV then the actual RPM displayed is accurate it is not running in V/Hz where there is no feedback adjustment for slip. The E510 does not have a pulse output function, the other option is just have a simple scalable voltmeter display and scale it to display the output as RPM.

Hall sensor is usually a straight forward install, in particular on a single or dual speed application, if there is a back gear then you need a switch to adjust the range. I have also placed a hall sensor and magnet ring on the bottom of the mill ram/spindle in combination with a ring LED light.

Back gear sensors, upper switch goes to the tachometer display.

Do you have additional pics of your magnet and sensor install? It appears you have the magnet mounted on the quill of your mill?

I’m beginning to think the route I was originally on may be too complex and possibly with a larger than ideal margin of error. Also, I’m wanting to get started on the install rather than spend weeks on study and testing. My drive can display RPM, but it’s remotely mounted inside a panel. Also, I’d rather not have additional displays (and consequently power cords) on the machine, I want all info displayed on my TouchDRO tablet. So…now I investigate the best magnet and sensor arrangement.

 

[Aaron_W]

If just an approximation at one specific pulley configuration this seems like busy work. You could simply list approximate RPM at each setting 1-10 and post it next to the VFD control.

 

[mksj]

Well aware that he wants to integrate the RPM into the TouchDRO, but I am also explaining that there are inexpensive simple options if it does not except that 0-10V input and there is not a simple solution to converting this back to a proportional pulse train output, which is the point of the discussion. Below is an example of a ring LED light with integrated hall sensor, as such it could be used with the TouchDRO, I have done this on a number of Bridgeport and other style mills. I did modify the design from the original, I found that if there is a close fit of the inner magnet ring to the outer sensor/LED light ring that it will induce a magnetic field in the aluminum that can effect the sensor reading. Attached revised design which is for the PM-935, but can easily be adapted to other types of mills. The ring LED light prevents shadows and I use one in addition to a strip light behind it mounted to the mill body. Cost of the sensor and LED is ring is about $10, requires a lathe (or a friend that has one . The alternative as I mentioned is there are very small LCD/LED voltmeters that one can scale the input/decimal places. I would check with Yuri as to if he has suggestions to convert the 0-10V signal to a proportion pulse train, oras mentioned put a scale on the speed pot. I would also explore if you can attach the hall sensor in the head of your mill and put a magnetic on the pulley, as I often also see this done if using a single speed system.

 

[Backporch]

I do believe the transmission is a great invention and so against my beliefs to aid and abet the full range VFD scheme ...but if you insist, have a look at a gizmo such as this V -> F converter board. Would require some electronic knowledge as these cheap Chinese modules have little to no useful documentation and since this one runs off a 15-24V supply, incorrect configuration could damage your TouchDRO interface. (You'd want to configure it to grounded-emitter, open-collector type output and let the TouchDRO input pull-up resistor take care of the positive logic level or better yet use an opt-isolator device to protect the TouchDRO board from the big, nasty VFD - if this language doesn't make sense - this is probably a bad idea). Don't know the upper frequency limit of your particular TouchDRO interface but if 10Khz is to high the module does claim to have some full-scale adjustment or just attenuate the analog output of the VFD for a suitable max frequency.

My plan (no yet implemented) uses four small Nb bar magnets held to the spindle with adhesive lined shrink tubing and a hall sensor attached to the nose piece. I plan to blind thread the nose piece for a small fastener to hold a small surface mount sensor module. Turns out that old style Sonicare toothbrush heads (with the threaded locking nut) use two perfectly sized (2.5 x 5 x 10mm) Nb magnets which are pretty easy to remove without cracking. Otherwise I imagine suitable magnets are pretty easy to find. Sharp Mill has a magic-belt style variable-speed transmission head so the VFD runs at full speed (except for jog and threading).

Did something similar on my VFD enabled lathe - works like a charm. Hardest part was finding the large diameter adhesive shrink tubing in affordable quantity (only need an inch or so).

Cheers, Louis