9411 signal timing

[RVallieu]

I am putting together a system to test encoders.  The NI 9411 looks to be a great fit to my needs with an R-Series PCI board and 9151 expansion chassis.

My question stems from one of the tests I have to run on the encoder signals - I have to verify timing offsets between the A and Anot and B and Bnot and Z and Znot channels - is there an existing property or can I access/configure the system using the 9411 to get me the information?

I have a feeling I will have to use something like use two 9229 Simultaneous AI modules, one for the "Regular" channels and one for the compliments as well as wiring into the 9411 for my other encoder tests.

[mishkin]

Ryan,

How good of a resolution are you hoping to get? With a digital module, you can monitor the state of the line and record a timestamp when the digital state of the line changes, then compare it with a time stamp from the other line to find the difference in offsets. However, there may be some values during transition (high to low) when the values are indeterminate, depending on how fast you're sampling. 

The way to go may be with an analog module, if you have one at your disposal. That will give you a better insight into the transition states.

[RVallieu]

The 9411 will have no trouble getting me the digitial transition times of the encoder signals when connected with the A, Anot, B, Bnot, Z, Znot - there is more than enough oversampling at the speed I will be running to accurately measure the transition times when connected as a normal encoder.

My question is can I access the Inverted channel signals alone to take a timestamp of their transition values as well as the non-inverted channel timestamps?

Looking over the documentation on the 9411 unit this does not seem to be possible.

I tried adding a virtual 9411 to a project - but it would not work. 

I have to verify that the "Channel" and "Not Channel" transition within a certain amount of time of each other.  I know I can get the measurements using an high speed simultaneous card - might have to go this route anyway for another test for voltage levels.

Message Edited by RVallieu on 04-06-2009 09:28 AM

[RVallieu]

Update: I got the 9411 added to the project.  I will have to explore some of the example code for the module.

[RVallieu]

Configuring Differential Input - how do you do this with the FPGA module?

I see that DIO0, DIO1, DIO2, DIO3, DIO4,DIO5 are available as input for the FPGA IO - but this does not jive with using the system for measuring differential digital inputs from the encoder.

Do I have to do a configuration in FPGA code or the project to set the module up for Differential Input?

Then if it is configured properly - would I only reference the DIO0, 2, 4 as the channels to verify differential line status (ON/OFF)?

[mishkin]

Ryan,

The 9411 can measure differential digital signals as shown in the manual (attached).  You should not have to set anything up in software and be able to read in differential signals as is. 

If you're using differential signals, you connect  you differential signals to DIx.a and DIx.b, where x = channel number. Then you will read either a high or a low depending on the voltage levels registered. 

If you wanted to do this in scan mode as oppoed to actually using the FPGA, you should have the RIO driver 3.0 or later installed, along with the RealTime module 8.6+