SSI jumps after a longer cable: drop the clock to match the length

After an SSI cable is lengthened or the cabinet is moved, position occasionally jumps to a huge number. Do not change the bit length first, and do not swap the rod first. On a long run the clock edge does not arrive cleanly — drop the rate to match the length. Series 16 SSI is 162; Series 19 is 192. The electrical table is the same; the mechanics are not. See 162 vs 192. Timing: Series 192 SSI.

Read the symptom first

• Occasional huge numbers, even at rest, worse after a longer cable or a cabinet move → drop the clock to the cable length, and check the gap between two reads.
• Jumps all the way along the stroke, but patterned → first check Gray versus binary on both sides. See SSI timing and Gray code.
• Quiet at rest, jumps only when moving → mechanics and magnet first. See signal jump troubleshooting.

Length versus maximum rate (same for 162 and 192)

Minimum clock spacing 48 μs. Count the whole cable, not the stub inside the cabinet. Beyond this pairing, edges degrade, the sample point walks, and you get occasional bad frames.

What to drop on site

1. On the motion card or PLC SSI master, step the clock / baud down one notch and see whether the jumps go.
2. Do not insist on 1 MBd beyond 50 m.
3. Twist clock pair and data pair separately; do not twist clock+ with data+. Earth the shield at the controller. See shield earthing.
4. Leave enough time between two reads. Too fast eats residual bits from the previous frame and also jumps large.

Match the connector to the output. SSI commonly uses D70; do not mix it with analogue plugs. See matching the connector.

Still wrong after the rate drop

Once the rate matches the cable, master and sensor still need the same bit length, Gray or binary, and clock frequency. Do not write 162 as 192. Output types: eight interfaces compared.