how to send an analog output signal on same axis running a stepping motor umi 7764/ PCI7334

[AZimmer]

I am running a single axis stepping motor (which is working fine) but for the application I need to be able to turn on and off a 5 volt laser.  It notes in the manual for the UMI 7764  that the the analog output can be used as a general-purpose voltage output.  I would like to use it as such, but can't figure out what VI's actually send messages to the board to output a 5 Volt signal.   Ideally I would use the analog output on the same axis that the stepping motor is on, but if need be I could use one of the other axis if this isn't possible (ie. it may not be possible to step and send analog voltage output on same axis at same time).  I have been looking at the configuring DAQ and ADC stuff, but can't seem to make sense if these actually control the analog output channel.  I think they just control the Analog input channels, but maybe I am wrong. 
Any help would be greatly appreciated
Andre

[Buechsenschuetz]

I am not sure whether it is a good idea to use an analog output as supply for a laser. We are using lasers in the sub-20mW range, and they typically consume 50 to 100 m-amps of current - I don't remember the specs completely but I am sure the analog output will not supply such a current.

I would prefer using any of the digital outputs to drive a PhotoMOS relay, and using an external supply for the laser (also the +5V host output of the 73xx controllers can't supply more than 100mA and should NOT be used as a supply).

[s_a_s]

To access the analog outputs from LabVIEW you need to use the LoadDAC.flx VI.  The Load DAC VI is used to send a value directly to an unmapped DAC resource. DACs not mapped as servo axis outputs are available for general-purpose analog output applications.  In other words, you will need to use a different axis from the one you are using for your motion to do your analog output.

Also, as noted in the above post, lasers are highly sensitive devices (especially diode lasers) that have very specific voltage and current requirements.  It is not recommended for you to power your laser from any source other than one approved for the laser.

[AZimmer]

Thanks for the info,

the laser we use is a simple construction level laser (runs on 3 AA batteries usually) and draws 22mA,  I like the idea of using a relay though and will do that.  Thanks also for clearing up the configuration of the ports, now I'll tackle that. 

Andre

[Buechsenschuetz]

> Also, as noted in the above post, lasers are highly sensitive devices (especially diode lasers) that have very specific voltage and current requirements. 


This is true as far as proper current control is concerned. This usually is provided by a (sometimes very simple) control circuit, measuring the output power of the laser diode via an integrated photo diode. That's why laser diode typically have three pins.

Of course you should never connect the laser diode directly to a supply - this will destroy it in micro-seconds (the LED crystal will still work but the laser mirrors will be destroyed). Even in laser pointers you will find a small control circuit, and any supply voltage should be connected to the input of the control circuit. Actually there are laser diode assemblies which will run even with unregulated supplies.

[AZimmer]

It turns out the PCI 7334 cannot send an analog output, only the 7344 can (needs to be a servo motor capable contoller).  Instead I am using a USB 6008 DAQ device to switch a transistor and supply power to the laser.  I could use the Digital I/O, but this would require an another interface device. 

[Giridhar_Rajan]

Hi,

It is possible to send analog output out of the same same DAC channel in which your stepper is connected, if you configure the stepper as open loop in MAX. I've tried it. This way you have the stepper output, analog output and encoder input acting independently. So you can use these seperately for different purposes, such as using the analog output for constant speed motors where speed or position control is not of much importance, encoder for positioning some other axes and stepper output for stepper control. With good programming skills, the NI motion controllers can thus be used for the most complex configurations. Great work NI !!! Nothing is impossible.

Regards,

Giridhar Rajan

Automation Engineer, Design

Cruiser Controls

Mumbai, India