Troulbe in measurement quadrature encoder with 6601.

[jimmyjimmy2000]

Hi,
We are trying to measure position with 6601. The frequency of quadrature encoder is from 100Hz to 8MHz. Now, we connet the A,B and Z channel directly to counter . Using the example in CVI, we change the filter to 100ns and use x4 mode. It works perfect at low frequency.
The problem is when the frequency of encoder is higher than 2MHz, the accuracy decreases greatly. I'd like to know about following:

1.Can 6601 do the previous task enough? Or I must change to use 6602.

2.If 6601 is available, is there any way to increase measurement accuracy ?(in software or wire connection )

[<Mike Ross> mross@smpcorp.com]

JJ2000,

There are some very interesting converters/interfacers for encoders (not NI products). Check out US Digital for some handy and economical items: http://www.usdigital.com/products/interface-products.shtml

http://www.usdigital.com/products/ecount/ is for an Encoder to Binary Number converter (24 Bit) $99.

There is an Encoder to Up/Down Converter: http://www.usdigital.com/products/pc6/ $16. Lots of other useful tools.

I don't work for these guys or anything, it is just that for the money they can be very handy tools. Other people make similar products.

For instance, you could get an Encoder Divider so the 6601 can keep working at higher speeds (lower resolution).

Take a close look at the Encoder to Binary Number un
it. For angle stamping data this could be much easier than working with 660x boards.

Mike Ross

[aasenjo]

Jimmy,

You would need to specify what type of accuracy you are looking for, which is pretty much dependant on the type of operation you are performing. You could be looking to timestamp your encoder positions or you could also be looking to perform position/angle tracking over time. You could also be performing single point vs. multiple point (buffered) operations. You could mention which one of the CVI examples you are using and that could give an idea of the type of operation you are performing.

The NI-6601 is able to perform quadrature encoder measurements and the only limitations you can have in regards of frequency are the filtering parameters (if you use filtering) and the actual maximum timebase of the board (20 MHz).

Please keep in mind that by ena
bling filtering at 100 ns you are only guaranteeing that pulses with widths of 100 ns or longer are not being filtered out. This limits your encoder phase frequency to around 5 MHz. (Each encoder period has a 50% duty cycle, therefore the pulse duration is half the encoder period). You can refer to the board�s manual for more information on filtering.

We would have to know the following in order to provide further help:

a) Type of operation being performed
b) Specific example you were using
c) Type of accuracy you were looking for
d) Range of accuracy you needed on your measurement

Regards

Alejandro Asenjo
Applications Engineer
National Instruments

[aasenjo]

I agree with Mike, sometimes signal conditioning might be useful when dealing with encoders. Based on the brief problem description I still don't see a specific need for it. We would have to wait for the details.

Alejandro Asenjo