Field Engineer’s Notes (From the Trenches)

The “Gotcha” is Shielding, Input Voltage Selection & Gate Logic.

Shielding / Wiring:​ A/B/Z are differentialsignals inside the module but single-endedto the encoder supply. Use shielded twisted pair: A with A,B with B,Z with Z\ (if used). Drain the shield at the ​ (or at the encoder metal housing if specified by encoder mfr — usually one end only to avoid ground loops). Keep encoder cables away from VFD power cables (>12″ separation or perpendicular crossing). A noisy A/B line causes “jittery count” or double-counting at high RPM.

Input Voltage Selection (5V/12V/24V):​ Set via software (Hardware Config → → Channel Parameters). A 5V encoder (TTL line-driver) will NOT work if the channel is set to 24V — you’ll see 0 counts. Conversely, landing 24V encoder signals with the channel set to 5V can damage inputs. Verify your encoder’s output type beforeapplying power.

Gate Input:​ The has a Gate input (Select A/B functions). If Gate is programmed as “Active Low = Count Disabled” and you leave it un-wired, counting may be inhibited. Either jumper Gate to +V (enabled) if not used, or program it as “Always Enabled” in the config.

Z (Index) Polarity:​ Program the Z input polarity to match your encoder’s Index pulse (usually Active High for most industrial encoders). If the Z pulse is present (check with DMM on DC or scope) but the counter doesn’t zero/preset on index pass, check the Z polarity setting and the “Action on Z” (Preset vs Reset vs Capture).

Real-World Applications

• Rotary Cutoff (Web Converting):​ A 2000-line encoder on the pull-roll feeds Ch1. Registration eye feeds the Capture Input. The captures the exact count at the mark; the CPU compares to the target cut length and adjusts the servo ratio. The ‘s Match Output fires the flying shear clutch solenoid at the precise count (= virtual cam). The 1 MHz rating handles line speeds up to 600 FPM on a 2000-line encoder.
• Conveyor Position Tracking (Auto Warehouse):​ Four channels track X/Y/Z axis position of a gantry crane via quadrature encoders on each drive shaft. The Cam outputs trigger “Slow Down” and “Stop” virtual limits 50mm before the hard mechanical stops, preventing overshoot without adding proximity switches along the rail.

High-Frequency Troubleshooting FAQ

Q: “MOD OK” is Green, but Count Value never changes despite encoder spinning.

A: Gate Disabled, Wrong Input Voltage, or A/B Wiring Reversed.

1. Check the Gate Input​ — if programmed as “Gate Active Low = Disabled” and left un-wired, counting is inhibited. Jumper Gate to the selected Input Voltage (+5V/+24V as configured) or set “Gate Control = Always Enabled” in the config.
2. Verify Input Voltage Selection​ in PME matches the encoder (5V TTL vs 12/24V). A 5V line-driver encoder on a 24V-selected channel = no count.
3. Swap A and B wires at the terminal block temporarily — if the count now changes (but direction reverses), your A/B phase relationship is opposite expectation (program “Reverse Count Direction” or swap A/B physically).
4. Check Z (Index)​ separately — if Z is programmed to “Preset Counter” and Z is falsely triggering (noise on Z line), it may be resetting the count before you see it change. Disconnect Z to test.

Q: Count “jitters” (+/- 1-3 counts) at standstill or jumps erratically at high speed.

A: Noise on A/B Lines.

1. Verify shielded twisted pair​ was used and shield is landed at ONE end only (preferably the TB ground terminal).
2. Check encoder cable routing — if it runs parallel to VFD output cables, re-route or separate. Add ferrite beads on the encoder cable near the if noise persists.
3. Ensure the encoder’s 0V (signal ground) is tied to the ‘s signal common (usually the same as the encoder supply 0V, landed at the TB).
4. Reduce input filter if available in config (some firmware allows filter adjustment) — but usually noise fix is physical/layout.

Q: “Fault” LED On or CPU reports “APU Configuration Error”.

A: Config Mismatch or Module Not Detected.

1. Ensure the is in the correct Slot​ as defined in the Hardware Config (Rack, Slot).
2. Download the Hardware Configuration to the PLC (Target → Download → Hardware). The needs its match registers, input voltage, gate logic, etc., downloaded from the CPU on power-up or via explicit command.
3. If using an RX3i rack, confirm the universal backplane firmware supports the (rare issue but check release notes for very old backplanes).
4. Power cycle the rack after downloading if the Fault LED persists.

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