encoder measurement

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coema
Posts: 3
Joined: Tue Oct 23, 2012 1:34 pm

encoder measurement

Postby coema » Tue Oct 23, 2012 1:49 pm

Dear all,
I recently bought a BLH motor (BLHM5100KC-A) and I connected it to a PLC.
I have some problems in getting the output speed when the motor is turning.
I would like to know:
1-- is the encoder provided with the couple motor+driver modirectional or bidirectional?
2-- What kind of signal I am supposed to read: for example the voltage, the frequency (it should depend on the motor speed, id it right?). What should I read from drivers' pins 2 and 3 (connector CN2) with a specific instrument like an oscilloscope?
3 -- Should I activate something to have the output speed or (as I think) it is enough that the motor is running?

Many thanks.

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om_tech_support_JT
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Joined: Fri Mar 12, 2010 2:59 pm
Location: Torrance, CA
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Re: encoder measurement

Postby om_tech_support_JT » Wed Oct 24, 2012 10:25 am

Hi coema,

Thank you for your purchase, and welcome to our technical forum. Please see your answers below.

For the BLH series, we actually use a hall-effect sensor on the back of a brushless motor. It is not an encoder. If you are interested in motors with encoders, please let us know.

The hall-effect sensor detects changes in magnetic polarity. We have a commutation magnet which rotates along with the motor, and we have 3 hall-effect sensors placed at specific locations which detects these polarity changes. These signals are converted to pulses. You can acquire speed information of the motor by connecting the SPEED output (pins 2 and 3) from the BLH driver to a pulse counter (not provided). The SPEED output will provide a pulse signal (similar to an encoder) with a resolution of 30 pulses per revolution. Since these brushless motor systems are designed for continuous duty, speed control type applications, the SPEED output does not distinguish between CW or CCW direction. Its purpose is for the operator to track and confirm the motor speed on another device besides the driver. The driver internally monitors the motor speed, and it will generate an alarm if it senses an error.

The SPEED output, like most of our brushless drivers, is a sinking, open-collector type output. This means if you connected an oscilloscope to pins 2 (SPEED output) and pin 3 (GND) and measured the voltage, you may detect little or nothing. You have to provide the voltage for our output. All the driver does for the output is open and close a transistor for each pulse. The transistor basically allows the voltage that you provide - into our GND. The voltage that you can supply our SPEED output is up to 26.4 VDC max and 10 mA max. Once you provide the voltage for our output, it will generate pulses whenever the motor is rotating.

I have included some graphics to help. These are also in the BLH series operating manual.
BLH SPEED output pulse signal description.jpg
BLH SPEED output pulse signal description.jpg (83.39 KiB) Viewed 13498 times

BLH, VEXTA brushless driver alarm, speed output circuit diagram.jpg
BLH, VEXTA brushless driver alarm, speed output circuit diagram.jpg (37.5 KiB) Viewed 13498 times

Let me know if you have any more questions.

coema
Posts: 3
Joined: Tue Oct 23, 2012 1:34 pm

Re: encoder measurement

Postby coema » Sat Oct 27, 2012 12:52 pm

Thank you for the quick and detailed answer.
I would ask you to send us, if possible:
1- an electrical schema of the output speed
2 the components’ characteristics (resistor value, transistor type, diode type) we could use having a 24 VDC as input Voltage
(as stated above our motor code is BLHM5100KC-A).

Many thanks!

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om_tech_support_JT
Posts: 1058
Joined: Fri Mar 12, 2010 2:59 pm
Location: Torrance, CA
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Re: encoder measurement

Postby om_tech_support_JT » Mon Oct 29, 2012 10:53 am

Hi coema,

I've already posted all the available information about our SPEED output circuit from the BLH series drivers. If you're trying to determine the R resistor value from our SPEED output circuit as shown in the diagram posted above, you can just use Ohm's Law, V=IR. If you are using 24VDC, then the R value should be: 24v=0.010mA*R; R=2.4Kohm. As long as there is a little bit of current flowing, our output would work. You can also measure the output current from your sourcing input (the one connected to our SPEED output), then determine the necessary resistor based on the measured current.

coema
Posts: 3
Joined: Tue Oct 23, 2012 1:34 pm

Re: encoder measurement

Postby coema » Wed Oct 31, 2012 3:11 am

I got it.
Thank you again for your answer, it was detailed and clear!


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