Encoder zero track high speed problems

[Kataeb]

We have an htl encoder connected (unipolar) to 2 inverters in parallel. After running smoothly for more than 2 months, a fault (F051) starts happening on the first inverter at a speed higher than 700 rpm.
After checking we found that the zero track is missing at high speed (we tried the speed loop without zero track and no fault happened).
We replaced the encoder by a new one, and the machine is now working ok.

Our concern is why this problem happened? And could it happen again?

The used hardware is:
Encoder, incremental, 1024 lines, 24 vdc, HTL, blind hollow shaft, connection cable, Sick (Stegmann), DGS66-HAZ0-S04
Connected to:
(x104) Inverter 18.5 kw, 37.5 A, vector, +CBP2+SLB Siemens 6SE7023-8TP60+ZG91+G42
(slot B) Inverter 11 kw, 25.5 A, motion control, +CBP2+SBP+SBP Siemens 6SE7022-6TP50+G91+C12+C13

Experience showed that usually siemens hardware does not like non-siemens parts…!

Thanks

 

[rdrast]

Misalignment? Dirt? Device failure?
Pick one.

Is there ANY device or thing in the world that cannot ever fail? Could a replacement fail again in the future? uhhh... yep.

 

[BryanG]

Also make sure that the load current is within specs. I had an encoder that would work long enough for the machine to be tested and sent to site only to fail in front of the customer . Turned out that the PLC manufacturer had changed the spec of one of the inputs and it was just on the limit for the encoder output circuitry.

The quality of encoder is important, some are lightweight in price and reliability, some you can strap to the outside of a submarine.

Alignment is vital, even using a flexible coupling to protect the system isn't enough. Check alignment, then check again.

One final thing, and though I don't have proof, I have seen it happen a few too many times to be coincidence. Some encoders don't like it if you use welding equipment on the machine that they are attached to.

Bryan