Lost counts from Linear encoder on cdaq9401

[Ingo1]

Hello,

I´d like to measure the postion from a Haidenhein 2571 TTL linear encoder with labview 8.5.
http://wwwpdb.heidenhain.de/ansicht/download.php?FilePath=..%2Fansicht%2FHeidenhain%2Fmedia%2Fimg%2F&FileName=MA_MT_2571_ID33526592.pdf

The encoder is connected to a c9401 card in slot6 of an c9172 rack, all other slots are filled with analog measurement cards.

The hardware setup seems to be correct, since a get a correct signal with buffered and unbuffered aquisition of the encoder data (i.e. samples from the labview samples library.

The problem is: This works only for rather slow movements of the linear encoder. With higher travel speeds a loss of counts occurs.
The maximum speed without losses is about 65000 counts per second.

I have tested this with an buffered aquisition using the cdaq1/aisampleclock whilst running an analog read task with the analog module in slot1 with sample speeds from 10-100khz and also with unbuffered aquisition.

Could this be caused by bad cabling from the encoder electronics to the 9401 card or is it more likely a problem with my labview Vi?

Thanks for your answers

Ingo

[JB]

What are the interpolation (x5 or x10) and the scanning frequency (25, 50, 100 or 200kHz) of the integrated digitizing and interpolation electronics ? Do you have a scope to analize the output signals of the MT 2571 ?

[Ingo1]

The encoder specifications are: TTLx5 , 100khz, which lead to vmax of 200mm/second according to its datasheet. I don´t believe i reached such high speeds during testing.

Do I have to adjust my labview VI to these specs in some way?

I may have access to a scope if the problem won´t solve but i also have another linear encoder for testing.

Ingo

[JB]

I would first check the hardware with a scope. The signals may be noisy, the levels may be wrong, the max output frequency of the length gauge may be reached... Do you also use the inverted signals ?

[Ingo1]

I don´t use the inverted signal yet. How can i do that?

I can only find the following connection plan in the DAQmx help:

A: PFI 0
B: PFI 2
Z: PFI 1

ingo

[JB]

This needs an external differential line receiver like the 26LS32. The usage of the inverted signals is recommended in case of noisy environment or long cables.
You will find a schematics on page 41 in HeidenHain's length gauge user manual.

[Ingo1]

Thanks for your support!

I will consider using such a differential line receiver if I encounter problems in the actual test setup.

But I hope the maximum speed will be enough for my measurement.