Heidenhain 11(micro)App sinusoidal linear encoders and USB 6009

[feanorou]

Hello, I need to read two Heidenhain 11(micro)App sinusoidal linear encoder signals, described here at page 37: http://www.heidenhain.com/fileadmin/pdb/media/img/208_945-28.pdf

I have been using a standard oscilloscope and merged the two signals on a two X-Y axis display, to display a circle to inspect if the glass scale is OK.

If the glass scale is OK, then the circle is relatively stable in size and position when moving the receiver along the scale.

Now I would like to do the same test with a USB 6009. Is it possible? Should the two signals be treated as analogic current input? In that case is 11 microA within USB 6009 specifications?

Thank you

Luke

[JB]

Have you considered to use an EXE 100 Series Interpolation and Digitizing Electronics from Heidenhain to convert the length gauge's 11µApp analog signals to TTL quadrature encoder signals ?

Using an appropriated DAQ board (unfortunately not the USB 6009), it is then very easy to get an up/down counter displaying the position of the gauge.

This document explains how to connect a quadrature encoder to a DAQ board.

[feanorou]

Hello, yes, transforming to TTL is a good suggestion for position measurement. Thank you for the link to the EXE.

If I just want to see the two analogic sinusoidal signals (without measuring position by counting impulses, for the moment) on the XY graph, will it still be possible on the USB 6009?  i.e. one signal in A0+ and A0- and the other in A1+ and A1- would not work?

Thank you

Luke

[feanorou]

I attach block diagram and front panel.

[feanorou]

The maximum analog input for overvoltage protection on the 6008/6009 is 35 V. The input impedance for the 6008/6009 is 144 kΩ. This would imply that the maximum input current during overvoltage conditions is 0.243 mA per analog input channel.

So, it seems that 11 microAPP are OK as current input.

Here the answer http://digital.ni.com/public.nsf/allkb/7D8EDCD0C3887EEA86257075004CE733

[Dennis_Knutson]

You are measuring voltages with the scope. You would of course want to do the same thing with the 6009.

[feanorou]

I am a real beginner in this. One way to measure AC current with an oscilloscope is to measure the voltage dropped across a shunt resistor. Since the voltage dropped across a resistor is proportional to the current through that resistor, whatever wave-shape the current is will be translated into a voltage drop with the exact same wave-shape. In this way I guess I could use two analog inputs of the USB 6009 for the two signals, but I do not know which resistance to use, i.e. to be in the range of 11microA, using max 5 V I should connect in parallel a min. 450kohm resistor?

How can I translate this in a USB 6009 pinout? 

Thank you

Luca

[Dennis_Knutson]

I'm confused about your wanting to measure current. If you have standard scope probes connected right now and the measurement is working, you are reading voltage. You would connect the 6009 to the same places you have the scope probes connected. This is a simple test you can quickly make. The 6009 can be configured for single ended mode. So, ai0 goes where you have scope probe one and connect the gnd of the 6009 to where you have the scope ground connected.

[feanorou]

Hello Dennis, unfortunately I do not have an oscilloscope. I was wondering if I can connect the sinusoidal curent signals to AIO+ and AIO- without using a resistor, just configuring them as current input, min. -20uA, max. 20uA, and terminal configuration as 'Differential'

Thank you

[Dennis_Knutson]

You said "I have been using a standard oscilloscope and merged the two signals on a two X-Y axis display, to display a circle to inspect if the glass scale is OK." 

It does not matter if you currently have a scope. If you used standard scope probes previously, then connect the 6009 in the same manner. If you used a differential probe, then fine, configure the 6009 for differential. Otherwise, configure it for single ended. No matter what, you cannot configure the 6009 for direct current input. It only supports voltage. If you previously used a current sense scope probe, then yes, you would need to put a resistor in your circuit. Please define what exactly you meant by 'standard oscilloscope'.