PCIe-6321 capabilities with BNC-2110 and BNC-2090A

[mori25]

Greetings, 

I am currently using a PCIe-6321 connected to a BNC-2110. 

My testing system is composed of a motor driver that requires the following parameters:

Motor movement: Frequency 300 Hz, amplitude 4.5V and a triangle waveform.
Motor circuit driver power: +-15V and 2A.

The system is working fine, without issues. I send a signal to the motor driver through the Analog Out (AO1), then on Analog In (AI0) receives a signal from the driver confirming the motor movement.

Since the current system uses 2 channels (1 Analog Out and 1 Analog In), the current Terminal Block BNC-2110 supports only 5 devices (motor drivers) connected to it.

Reading the datasheet specification for both NI products, I was wondering how much the maximum current delivery per channel (Analog Out) is. For example, since I am sending the same signal to all the motors, if it is possible, to have one Analog Output connected to several (3 or 4) motor drivers.

In case it is not possible, then the option is to “expand” the testing system using the PCIe-6321 connected to a BNC-2090A and then in daisy chain with the BNC-2110. If possible, I would like confirmation of whether the current system is supported.

Reading the documentation from all the equipment here commented, it is compatible, however a double check is always welcome, since I am not completely familiar with this equipment.

Thank you very much.

[Kevin_Price]

The 6321 spec sheet appears to say that each of your two AO channels can source 5 mA.  So for sure you'll be limited to 2 distinct output waveform shapes.  Whether you can split one channel out to multiple drivers will depend on how much current the drivers draw.

There are simple circuits available to mirror your output voltages while being able to source a lot more current.  I don't dabble with such electronics myself all that much, so I'd better leave it to someone else around here to give a specific recommendation.

-Kevin P

[NathanDavis]

Hello mori25

I’d agree with Kevin_Price that the “unity gain buffer” circuits would work well in your case.

But before that :

Currently, when you’re using the setup consisting of a single motor i.e. the analog output driving one motor with analog input measuring the response.. have you measured the current draw coming from the analog output? Placing an ammeter in series with the output of the analog output?

This will give you an idea of how many additional motors you can drive with your analog output channel. For example, if one motor requires 1 mA of current draw from the analog output.. then assuming all motors draw the same amount of current, you can ideally place five motors on the output drawing a total of 5 mA (as outlined by Kevin_Price above). Though, I wouldn’t push the limits of the card, stick with four motors, say.

I would assume the motor drivers you have contain high impedance buffers only requiring a few hundred microamps of current. Then your +-15 V power supplies take the brunt of the current needs.

As far as the analog input channel(s), assuming each motor is putting out an output voltage to confirm that the motor has moved: Is this a binary voltage (i.e. 0 V and 5 V), buffered voltage (same as input showing the voltage was present to the motor), or some current proportional voltage to how much current a single motor required to move?

Also, as a failover mechanism, if any of the motors aren’t working properly (as measured by the analog input), you may consider using digitally controlled switches (with reverse diodes) on each motor to isolate.

Depending on your requirements, I would recommend checking out motors and motor drivers created by Pololu.