I'm trying to use the pseudo tach feature when collecting data for an intermediate shaft in the gearbox using CSI2140. The motor constantly changes its speeds while running (ramps up, slows down and stop to make one cycle) controlled by a VFD. Will the pseudo tach feature work on this application? I put in the correct input/output ratio or tooth count but the detected running speed of the intermediate shaft in the software doesn't seem to be correct. Will the pseudo tach work on variable input speeds?

Original Post

Either way, the ratio or tooth count used. As the intermediate shaft cannot be directly tached, I attempted to use the pseudo tach option while taching the motor shaft. If the motor has constant running speed then the pseudo tach will work based on the correct given speed ratio or tooth count. What about a motor that is changing its running speeds while collecting data, will the Pseudo tach somehow show the order tracked running speed as the motor shaft is being tached

I can't say specific to 2140, but in the olden days:

Do you have a tachometer on the motor shaft? If yes, then for machine setup choose Enter Speed only Once =  No, and Check/select on Fixed Tach Location

The Motor shaft speed Reference and each measurement point Reference (ratio accordingly) are part of the Measurement Point setup.

The intermediate measurement points on gearbox would then have the speed ratio to the actual motor speed. It would be wise to make all measurements on machine at close to the same motor speed; during one survey and repeated surveys. The old apples-to-apples comparison game!

Walt

Thanks all. Yes, I use a tachometer to measure the motor speed at the motor outboard cooling fan (this is the only place to measure the motor speed). Even if the machine RPM is put in as 1720 RPM (for example), this is never the true turning speed and the motor changes its speeds while collecting data. Using "fixed tach location", will the speed of the intermediate shaft be changed proportionally based on the ratio added to the reference RPM?  As I'm using a tachometer, will the software auto calculate the speed of the intermediate shaft based on the ratio? Pseudo tach option is not needed with this fixed tach location?

"Using "fixed tach location", will the speed of the intermediate shaft be changed proportionally based on the ratio added to the reference RPM?  As I'm using a tachometer, will the software auto calculate the speed of the intermediate shaft based on the ratio?"

Yes. For example: Motor Reference speed is 1800 and Fan Reference speed is 900 rpm (0.5 ratio). Say actual motor speed from Tach is 1600 rpm (overwrites 1800), then fan speed would be scaled to 800 rpm when measurement is made.

No knowledge of the Pseudo Tach option. If someone has a 2140, then they could comment on this feature.

Walt

"

F2 Pseudo Tach

"Enable Pseudo Tach for time synchronous averaging or order tracking intermediate shafts in gearboxes that cannot be accessed directly. Use the Pseudo Tach to produce the turning speed signal. The analyzer uses the following formula: (Incoming tachometer frequency) X ((tach frequency X the number of teeth on the tached shaft)/number of teeth on the pseudo shaft). Disable Pseudo Tach when you can use the tachometer directly on a shaft. The default is Disabled."

I guess CSI makes it more complicated than necessary! If your tachometer frequency is based on a 1/Rev shaft target on the motor shaft, then the Intermediate shaft rpm is the ratio of INput/OUTput gear teeth. If your tachometer frequency is based on a N/Rev (pinion gear teeth), then the INput speed (pinion or motor) is Tachometer frequency divided by the number of teeth (N). It follows that the Intermediate speed is still the ratio of the number of teeth on each shaft.

I can't add any more than this, so you just have to try it!

Walt

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