Oscilloscopes

An oscilloscope is needed when replacing or aligning an encoder assembly. This page contains information about the two oscilloscopes most commonly used by Creo Customer Support.

Fluke 99B Scopemeter
Tektronix TDS 200 series

Tips on using them: Oscilloscope selection |  Tips and techniques

Oscilloscope selection

High bandwidth is not a requirement for an oscilloscope being used to align encoders. The frequency of the analog signals A+, A-, B+, and B-, are only 27 kHz when the drum is spinning at 180 rpm! An oscilloscope with a bandwidth of only 20 MHz is more than enough for encoder alignment. A 100 MHz oscilloscope will be no better for this task, and it costs significantly more.

Triggering is quite important. Some inexpensive oscilloscopes do not do triggering very well, making encoder alignment almost impossible.

Digital storage scopes are better than analog scopes for viewing the index pulse. There will only be 3 index pulses per second from a drum spinning at 180 rpm, so it is difficult to see it with an analog scope.

Tektronix TDS 200 series (part number 90-1106)

These scopes, which are portable with LCD displays, are easy to use and relatively inexpensive. The controls are very similar to Tektronix CRT scopes, so if you have had experience with analog oscilloscopes, you can learn to use this one quickly.

More information on these oscilloscopes is available on the Tektronix web site.

Fluke Model 99B Scopemeter

This model is also good for encoder alignment. It has more features than the Tektronix scope, but is expensive and more difficult to use. Earlier models were 50 MHz; newer ones have a bandwidth of 100 MHz.

More information on these oscilloscopes can be found on the Fluke web site.

Tips and techniques

1. Viewing the index pulse - There will be one index pulse per revolution of the drum, so proper triggering is critical. You must ensure that the trigger mode is set to "Wait for Trigger" (Fluke scope) or "Normal" (Tektronix). In this mode, the trace will only start when an index pulse triggers it. If the trigger mode is set to "Free run" (Fluke) or "Auto" (Tektronix), the trace will sweep continuously whether there is an index pulse or not. If this is the case, the index pulse will be hard to see if you can see it at all.
2. Autosetup - this is fine for repetitive signals such as TachA or TachB, but it won't work for the index pulse.
3. Fluke 99 setup files - If you have a Fluke Scopemeter, the optional serial interface adaptor, and the optional Flukeview software, you can load Scopemeter setup files from your laptop. Download and unzip Fluke oscilloscope setup to a directory on your laptop.  The two setup files will set all parameters in the scopemeter as follows:
   • phmeas.set Setup for adjusting the A+, A-, B+, and B- signals with phase measurement. This setup file will set the Scopemeter to 200 mW AC/div, 50 µS/div. and it enables the measuring cursors. The cursors will measure and display the phase difference between the two signals on channels A and B. You can remove the cursors by pressing "Sub Menu", then F5 (cursor reading).
   • index.set Viewing SI (Index) on the encoder block test point. Connect channel A to the SI test point on the encoder. Channel B can be connected to either SA or SB. You can also use this setup to view the TachI signal on the MPE board test point. Just change the trigger slope from "-Slope" to "+Slope". This is a general setup that will also work for viewing SA, SB, AD, BD, TachA, and TachB.