usb 6009

[makk]

Hi,

I am generating a PWM signal. My VI is working well. But the signal is showing upto 1.08volts only. but i want to use till 4volts. how can i change this value. Even i attached my DAQ assistant dialogue box, which is showing Voltage output as 1.1V(Red Circle). I have seen this signal on oscilloscope connecting through Analog out AO0. Please suggest how can i change that voltage out value.

Thank You.  

[johnsold]

1. The USB-6009 has software timed AO and DO so it is not really suitable for PWM.

2. If you are doing PWM, why do you want to vary the output voltage, other than high and low?

3. The AO lines are limited to 5 mA. At 1.1 V a 220 ohm resistor will draw that much current. For 4 V the resistance must be >800 ohms. What is your load impedance?

Lynn

[makk]

Hi Lynn,

        Thank you so much for your reply. Actually  i'm controlling the speed of a dc motor. For that pupose i'm using half bridge. Through that AO0 port im applying duty cycle to half bridge, so that i can contrlo the motor. But my DAQ is showing only 1.08V. so please on this issue.

[johnsold]

Sounds like the voltage drop across 2 diodes and a motor winding.

Unless the motor is so small you need a magnifying glass to see it, you CANNOT drive it with the USB-6009. Most motors require much  more current than the device can provide. You will need some kind of amplifier or motor controller between the USB-6009 and the motor.

What are the specifications (voltage, current , power) for the motor?

Lynn

[makk]

Its a DC motor with  the following ratings

          Voltage 24V,

          Current 3.3A and

          Power as 44W.

   So suggest some good idea so that i can work with USB 6009.

[Dennis_Knutson]

I'm confused. You said you set the output in the DAQ Assistant to 1.1 volts.

[johnsold]

First you need to learn some basic electricity. The maximum output of the USB-6009 is 0.005 W. Your motor requires almost 10000 times that much power. The chances that you will destroy some expensive equipment are quite good when you do not understand the basics.

You need an amplifier or motor controller which is suitable for driving your motor. Find one which accepts an analog input voltage from 0 to 5 V and you can use it with the USB-6009.

Although PWM is an efficient contrl method, the USB-6009 is too slow to be a good PWM controller. The motor speed would vary from moment to moment in a very jerky manner.

Lynn

[makk]

Let me explain you clearly. My aim is to see Voltage, Current and Speed signals of the dc motor.

For voltage, I’m using a voltage divider. Because the DAQ will not handle the 24 volts. That’s why I’m using voltage divider so that I can see 5V signal on labview screen.

For current signal. I’m using shunt resistor and for speed I’m using encoder. Till now everything is ok and I’m able to see the signals on labview screen.

Now I’m trying to control the motor at least 10% so that I can prove that USB6009 can controls a DC motor. So that I’m using a single transistor with one diode and one resistor. This is shown in the attached schematic.

The working principle of the circuit is very simple. The BJT transistor act as a power switch for the motor. The switch can be controlled through the voltage. When 3V-5V is applied, the transistor is turned ON and the motor is connected across Supply voltage Vcc and ground. So the motor will run.

[makk]

Here is the scematic. If the Analog out gives 4v to that transistor. then the motor will start . but my DAQ is giving only 1.08v. how can i increase this voltage. because Analog Out limit is 0-5V

[crossrulz]

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@makk wrote:

Here is the scematic. If the Analog out gives 4v to that transistor. then the motor will start . but my DAQ is giving only 1.08v. how can i increase this voltage. because Analog Out limit is 0-5V

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The analog output can't put out enough current.  You need an amplifier.