I was hoping for some insight into very intermittent yet continuous entrapments on 2 out of 3 units. Entrapments always occur between floors with a drive unit fault 99. Fault 36 always proceeds fault 99.

Both problem units have had the tachs replaced and calibrated. New drive setups done. Pulse scale is within spec +/- 5 of 250.

All voltages and contacts have been checked, yet I’m thinking it must be a flakey contact or a voltage value slightly off. Or pulse board?

Any thoughts would be greatly appreciated.

Are the units SCD drives? If so what speed are the cars? Geared, Gearless? 4MS 500-800 fpm, would be 250 PPM. if it is 2MS the value would be 500 PPM.

Thanks for the response.

The units are a very old Otis gearless, double wrapped 1:1. They are running 500 fpm with the scd drive. We do have the laptop to hook up as well.

Do you do high speed nulling on the tachs? Anytime you touch a tach pot on the A3 Board you must run a new floor table. Tach belts have to be tight so they don't slip on pulleys. Look for oil or anything leaking on belts. It leaking on belts, they are slipping. Put car on inspection and pull on tach belts, if they slide over the pulleys they are too loose. Make sure you have all the belts on or they will slip also.

Hi Rolly,

Thank again for the response. I’m sorry I’m not familiar with the high speed nulling procedure. We adjusted the tachs offset to each other and scaling on inspection speed. The tach bands are tight, but could possibly be tighter.

Maybe a silly question but, is drive fault 99 (excessive tach error) strictly related to the tachs? And is error threshold adjustable

Never saw that error, drives were never a problem. You need to null each tach individually to close as possible to zero volts. Car inspection speed is 78FPM. Main tach is meter on MP7/A6 to Potential earth, zero using P2/A3 and supervisory tach is Meter on MP1/A3 and adjust P5/A3. After touching pots, load new floor table. Make sure belts are tight before you start.

Thanks for all the input.
I swapped out one of the tachs on the most problematic unit this afternoon. I also added 2 polycords(only had 6 out of 8).
Adjusted insp speed and pots as mentioned, performed learn and the pulse scale came in at exactly 250!

Time will tell.

Thanks again

A little tip about nulling tachs. A fast meter like a Fluke 87 or above is needed. Use volts, not millivolts, and move the range over 2 decimal places. Much easier to see what's really happening.