No pulse at step(CW) output

[ANRAD]

I'm using Measurement & automation Explorer and trying make my stepper motor turn. I've eliminated the stepper & its drive as a problem. I can't measure anything resembling a pulse at the step(CW)1 terminal of the UMI-7764. I configured M&A explorer to give me a pulse per second but measuring 0.124V all the time. ALso my direction terminal is reading 1,625V...what gives?

[Koninika 73]

Hello,
Make sure you are powering the UMI-7764. Are you able to get your motor to move when you give it a target position in Measurement and automation explorer (MAX)? Also, you can check the step and direction line during motion. When you move forward you should see the direction line going one way (high to low) and then as soon as you give the target position to move backwards the direction line changing and going (low to high). Also you should notice a pulse on the step line.
There is also a inhibit output line on the UMI which can be tested. If you toggle between kill and halt in MAX, you should notice the output on the inhibit line also toggling. Most of the drives have an enable line which is connected to
the inhibit output line and needs to be enabled in order for the drive to provide power to the motor. Are you in open loop or closed loop mode?
Please let me know if you have further questions.
Good luck and have a great day!
Koninika
Applications Engineering
National Instruments

[denyart]

I am using the 7774 UMI interface. I have it powered with a 24VDC supply, as well as a separate 5VDC ISO supply . I have the exact same problems as the original post. My motion controller is a 7334 PCI card. I am trying to send moves in MAX, but it shows the moves with no actual motion occurring. I checked the step output, and referencing it to the digital ground (or ISO ground) I don't get any voltages high enough to register as active high. I also looked at the step pulses on an oscope and they were only 0.2V and not "square" (if that is what they are supposed to be. Any help on how to wire this (i.e. what exact pins should you use for the Step- and Dir-) UMI would be great. Thanks

EDIT: I have rechecked the step and direction signals with a different scope. Now I can clearly see the step square wave pulses. They look fine. I am running them into a drive unit with standard DB25 controller inputs. They have optically isolated inputs. If I hook the step signal's step- to a common ground (the ISO common) I still get nice 5V square pulses. If I tie in the Dir- wire to this I loose most of the signal (down to ~1.5V). It seems that the Dir- wire from the drive unit has ~3.5V bias that mirrors the step signal. Does anyone have any idea how these things need to be wired to get the step and direction inputs on the drive unit to see the step and direction signals properly from the UMI7774?

Message Edited by denyart on 03-28-2006 12:28 PM

[David S.]

Hi denyart -

The Step and Dir pins on the UMI-777x are direct passthroughs from your PCI-7334 controller.  The NI-7330 Hardware User Manual's specification for these output is open collector with a built-in 3.3kOhm pull-up resistor.  These signals are also referenced to the Digital Ground pins on our units, not the Isolated Ground.

I'm not sure why you're connecting the Dir- input on your drive to the Step output on the UMI.  I would assume that, if your drive has differential inputs (such as Dir+, Dir- or Step+, Step-), you would connect our Dir output to Dir+ and our Digital Ground to Dir-.  Am I misunderstanding the setup?

Any pinouts or user manuals you have access to will help troubleshooting too, so we can see exactly what you're trying to connect.

[denyart]

My drive has optically isolated step and direction inputs. I needed to modify the connections, because the obvious connection would not work. The 7334 cannot source enough current to turn on the optical coupler diodes. I got a response from a phone call to NI that resulted in this.

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z0000019UmRSAU&l=en-US

A different article that was listed here

[broken link removed]

went into more detail. I used method 1 from this second article to make my system work. Now with 200ohm resistors in series with the step and direction circuits, and hooking the step- and direction- wires to the Step and Dircetion pins on the UMI 7774 and a 5VDC power (from pin 3) to the step+ and dir+ I am able to make it work. My only question that remains, is whether this is the complete right way to make this work, or should the step signal be set to active low to work properly. In other words, am I triggering a step when the controller means to send a step, or am I triggering a step when the controller is supposed to be "in between" steps? I also wanted to know if there is a way to limit the stepper card to 200ns minimum step duration and 200ns minimum rest between steps, because if it ever goes to the 125ns pulse that is listed as the minimum, my motor driver supposedly will not recognize it. The step pulse requirements are 200ns minimum duration with at least 200ns between pulses. 3.2V min to 5.2V max. 6.2mA min and 15mA max. I also am supposed to wait 50microseconds after the direction signal is changed before I start sending step signals (for a different PMC LN2 motor amp/driver).

Thanks

[David S.]

Hi denyart -

I'm glad our KnowledgeBase article got your app working.  In response to your two specific questions:

1. I recommend setting the signal to Active Low.  Because you want the open-collector output to sink current from the interface circuit during a step, setting it to Active Low will make sure the drive reads a step when it is commanded.
2. There is no way to enforce the pulse width on our controller output.  The specification given is defined by the hardware on the controller, and that cannot be modified.  If you see the drive missing steps, you may have to contact the drive manufacturer for recommended workarounds.
   

[denyart]

Okay, I set it to active low and measured the Step- signal with a scope. The signal goes from +5V in between pulses to nice 0V square pulses when it steps. This should cause the Step+ to see a +5V square wave since it is always at +5V potential. The original article did not mention changing this setting, but I think it is the right way to set things. The stepper did work without it though, but I imagine it was "stepping" when the controller was going to the in between part of the signal. I also tried some very fast motion settings and measured the pulses at 200ns. This would be a prolem if I ever stepped this fast, but it isn't likely in any of the work we do. Thanks for the help, and I look forward to the rest of the development for this system.

BTW:Could you point me to any help with controlling an oscope for data aquisition in an automated "c-scan" ultrasound type of system?

Thanks again

[s_a_s]

Hi,

The best place for answers to your instrument control questions would be the Instrument Control (GPIB, Serial, VISA, IVI) forum.  You should be able to find the answers to your questions about controlling your o-scope there.