NI 9269 Analog Output Module

[Gilfoyle]

Hi,

My motor driver runs between 0-10 Vdc. And I am controlling it with NI 9269 Analog Voltage Output Module.

According to my motor specification, the maximum speed of the motor is 45000 rpm.

Then can I make a scale that tells me that the RPM of motor is 4500 at 1 Volt or 2250 at 0,5 Volt or something else?

Actually I did, but the thing I wonder is that this scale gives me correct RPM value???

Note: error in between 0-100 rpm can be ignored

[TheOtherKid]

Hey sefaa,

Its going to be a little more complicated than that in general, and it will also depend on the type of motor you're working with. It sounds like you're working with a brushed DC motor, but a datasheet would be helpful. Can you post a link to the specs for the motor you're using?

There are a few things I can say right now though:

1. Most motors at that voltage range will draw at least 0.5-1A when a load is applied (some of them will draw that without any load), and the 9269 is only rated to put out a few milliamps of supply current. It's really designed for low current applications that don't work with an inductive load like a motor. In short, unless you are 100% certain you can drive that motor with your current set up, do not connect the motor to that module. You could potentially damage your hardware if you do.

2. Motor speed depends on many factors besides applied voltage, most notably: supplied current and drive load. This makes it difficult to get an estimate without a feedback loop of some kind. If you want any level of accuracy at all, I recommend finding a motor encoder to measure rotational velocity.

3. It sounds like you need to get a motor driver/controller. The most important consideration for that would be the current draw of the motor, particularly the "stall current" in the datasheet.

[Gilfoyle]

I attached my motor driver datasheet. 

Right now, there is no problem. I can control the motor with NI 9269. I just wanted to see RPM by making some manipulation or calculation. To make a scale made me sense, but load resistance or load current can effect as you said.

It is ok. I just wanted to learn whether I can. 

Thanks 🙂

[TheOtherKid]

So, this device is actually a lot more than just a motor. It's a motor driver with a lot of different capabilities, including connecting to encoders (pg 4-23). If you're trying to get any kind of determinism or accuracy in relation to the output rpm, I recommend getting some encoders.

As far as which encoders to use and how to use them with the device, I recommend referencing the manual and/or contacting the manufacturer if you need more information. They might even have a recommended encoder that you can use with their device.

If you don't care about accuracy, you can figure out the rpm at your maximum voltage output, this would be approximately 4500 with no load applied. Then, you can lower the voltage until the motor stops rotating and call that the zero value. Afterwards, you can assume that the rpm's increase linearly with increased voltage. This will be very inaccurate (I can't say for sure how much so), but it will give you a vague approximation.

[Gilfoyle]

Sir, we read RPM on the screen of the motor driver. Also we read the value motor's driver program. But since we control the motor driver with LabVIEW, we also want to observe RPM value on LabVIEW. So we do not want to use motor's driver software. This is main purpose.

I made a scale. It is easy. Each 0,05556 Vdc means 250 RPM. But! The error seems more than 100 RPM according to the value that is read from the screen of motor driver.

Actually we do not trust the measurument of motor driver since even though we remove encoder cable, it goes on to measure the RPM knowladge. It is an interesting issue.

So we connect a RPM sensor. Now we measure the RPM value with the sensor. But since we do not have required module, we can not observe the information on LabVIEW.

But if you say that I may read the RPM value making a Voltage-Speed scale on LabVIEW with approximately 100 rpm error, then I will use the scale by removing the sensor???

Since my knowladge is not good about this subject, I can not be sure.

[TheOtherKid]

I might be a bit confused on this one. You have an encoder but you can't read it in LabVIEW? Are you not able to interface with it through the driver?

I can't really give any kind of value for the error you'll see from dead reckoning the rpm. Aside from a few exceptions, motors don't work in such a way that you can estimate the rotational velocity without measuring it. I simply mentioned that method as a way to get a vague idea of how fast the motor is going.

My recommendation is that you try to find some way to use an encoder if at all possible.