Troubleshooting Renishaw NC4tx on Heidenhain TNC 640

A non-contact tool setter has two independent paths: the optical/interface path reports whether the beam is clear or broken, while the CNC cycle path converts that state transition into tool length or radius data. A successful calibration proves only that the calibration path can locate the beam and write its results. It does not prove that a measurement cycle can retrieve the active tool record, validate every cycle variable, or interpret the interface transition correctly.

Measurement and calibration mechanism

The NC4tx beam state passes through the NCi-6 interface before the TNC 640 cycle evaluates it. The term drip rejection here means suppression of transient beam interruptions caused by coolant droplets. An incorrect interface-switch configuration can therefore make a valid tool crossing appear to occur at the start of the measuring move or at an otherwise invalid point.

The documented installation presented two distinct faults. Setting NCi-6 SW1-3 to ON allowed measurement to operate, identifying interface configuration as one fault. Later testing showed that only the tool in the first tool-table row could be measured; every other tool crossed the beam, stopped, decelerated the spindle, and produced 160-00AE Invalid value. That second result identifies a cycle-data or tool-record selection fault rather than an optical fault.

Observed symptom	Primary branch	Next check
Calibration and measurement both miss beam changes	Optical alignment, interface output, or PLC input	Check LEDs and the converter output
Calibration passes, but measurement reports an initial beam crossing	Interface mode or transient beam rejection	Check NCi-6 switch settings, especially SW1-3
Measurement stops with 160-00AE	Illegal value assigned to a cycle variable	Correlate the failure with tool row and cycle inputs
Only the first tool-table row measures successfully	Active-tool lookup or table indexing	Trace the active tool number and selected record
Error requests correction of REN_.TAB rows 40–42	Beam-axis, radius-axis, or length-axis mapping	Validate those mappings against machine kinematics

Check 1: Optical and interface state

1. Observe the emitter/receiver indication with the beam clear. Expect the normal clear-beam indication; the installation used green LEDs for this state.
2. Block the beam deliberately. Expect the indication to change to red and the output from the converter module to change state.
3. Read the same transition at the CNC or PLC input. If the interface changes but the control input does not, trace the interface output, wiring, input assignment, and PLC logic before changing cycle parameters.
4. Compare the switch positions on the installed NCi-6 with the interface instructions for that exact configuration. The hardware can have more than one configuration, so record every switch position before changing one.

If all three signal observations change cleanly, continue to Check 2. If the beam indication flickers or changes without a tool crossing, remove contamination and investigate transient rejection. Do not use calibration success as a substitute for these readings.

Check 2: NCi-6 transient rejection

Set SW1-3 only according to the installed NCi-6 configuration. In this installation, changing SW1-3 to ON made measurement work after calibration had already been passing. The practical mechanism is that drip rejection prevents a short coolant-related beam interruption from being accepted as the measuring edge.

1. Record the existing SW1-3 position and the clear/broken beam indications.
2. Apply the documented switch position and repeat the same measurement under the same feed override and spindle conditions.
3. If the cycle no longer reports that the beam was crossed at the beginning of travel, retain this branch as an interface correction and proceed to tool-row testing.
4. If 160-00AE remains, note whether the tool physically reaches and crosses the beam. A clean physical crossing followed by an error moves the diagnosis to cycle-variable validation.

Do not treat SW1-3 as a universal cure. It corrected one behavior here, but measurement of non-first-row tools still failed afterward.

Check 3: Error 160-00AE and cycle inputs

160-00AE Invalid value means that the control attempted to assign an illegal value to a variable. The prescribed correction is to edit the NC program, but a measuring-cycle failure can originate in an input supplied by the program, a Renishaw configuration table, or a tool record consumed by the binary cycle.

The diagnostic pointed to block 894 of length.cyc. Because the installed .CYC file was binary, editing or decompiling it is the wrong diagnostic starting point. Identify which external value changes between a passing and failing call.

1. Capture the complete cycle call and every displayed parameter for a passing tool.
2. Capture the same data for a failing tool and compare only the changed fields: tool number, table row, preliminary length, diameter, result mode, offsets, and active table.
3. Verify the definition of each Q parameter in the help belonging to the installed cycle revision. The local descriptions of Q380 were contradictory: it was described as a result-selection field in one place and as a length with an allowed range of 30–300 mm in another. The installed cycle help and input dialog decide which definition applies.
4. Check Q366, shown locally as a preliminary-length value for length cycle 503. Enter a value with the units and range requested by that installed cycle, not a value copied from another software revision.

Check 4: Active tool and table-row selection

A result that depends on table position is a strong discriminator. When the first row succeeds and another row fails after the same physical beam crossing, the optics, interface, beam coordinates, and basic measuring motion have already performed their common functions. The changed element is the data selected for the active tool.

1. Create a separate test tool record while leaving the calibration artifact in the spindle.
2. Enter an approximate physical length and diameter for that artifact. This prevents an empty, zero, out-of-range, or unrelated field from entering the measuring cycle.
3. Measure length and diameter separately. For the diagnostic calls, use a length offset of 0.5–1 mm and a radius offset of 0.
4. Run the same call first with the known passing first-row record and then with the new record. Keep spindle contents, beam, feed override, and offsets unchanged.
5. If only the first row passes, trace the current tool number through the tool table, spindle record, PLC state, and any tool-changing tables such as wzw.tab. Confirm that the cycle receives the intended active record rather than a fixed first-row index.

Also compare spindle rotation during calibration and measurement. The calibration artifact was measured from below, above, and from both diameter sides, with rotating and non-rotating phases. A measurement call that starts rotation and crosses the beam has progressed beyond basic spindle-start and motion initiation.

Check 5: Renishaw table configuration

Messages naming REN_.TAB rows 40–42 direct attention to the configured beam axis, radius-measuring axis, and length-measuring axis. Read each row and compare it with the actual machine coordinate system and approach direction. A valid calibration position does not make an incorrect measurement-axis selection valid.

In TAB_1.REN, parameter 14 was shown as APPROACH METHOD, where 1 means no tool data and 0 means tool data required. Changing it from 0 to 1 is a useful isolation test: if non-first-row measurements then run, the failing branch is the preliminary tool-data lookup. It is a diagnostic choice, not a substitute for repairing active-tool selection when production measurement requires tool data.

Review the configured motion values as a group. The installation contained 20 +20000 for repositioning feed rate, 21 +30000 for feed to maximum tool position, and 22 +15000 for feed to minimum tool position. Confirm their units and suitability against the machine's configured limits. These values affect motion behavior but do not explain a tool-number-dependent illegal variable unless a selected record changes the calculated target.

Check 6: Cycle-package consistency

Calibration and measurement cycles must belong to one compatible installation package. This setup referred to cycles 503 and 512, while the diagnostic entered length.cyc. A manual or parameter map for a different cycle generation can assign different meanings to the same displayed field.

1. Inventory the installed programming manual, installation manual, Renishaw error files, system test programs, PLC configuration files, table files, cycle programs, and cycle-tree files.
2. Where present, compare the package identifiers for H-2000-6680.pdf, H-2000-6681.pdf, REN_TNC, PLC_FILES, TABLE, CYCLE_PROGRAMS, and TREE1 through TREE5. The objective is one coherent set, not merely files with plausible names.
3. Run the supplied system or service test programs before editing production calls. Record which test first fails and the active tool record at that point.
4. If the table format and cycle help disagree, install or restore the matched package supplied for the controller and machine integration rather than modifying the binary cycle.

Resolving procedure

1. Prove the clear-beam, broken-beam, interface-output, and PLC-input states.
2. Record all NCi-6 switches, then apply the documented SW1-3 setting. Repeat the measurement at 100% feed override, using the same override for calibration and measurement.
3. Validate REN_.TAB rows 40–42 against the physical axes.
4. Confirm the installed meanings and ranges of Q366 and Q380. Correct the NC call that supplies the illegal value.
5. Test TAB_1.REN parameter 14 with the no-tool-data approach to isolate the lookup branch.
6. Compare identical measurements using the first tool-table row and a second populated row. If the first passes and the second returns 160-00AE, correct the active-tool index, table reference, PLC state, or mismatched cycle package.
7. Restore the production approach mode after the intended tool record is selected reliably.

Numbered verification checks

1. Check 1: With no obstruction, expect the clear-beam indication and its corresponding stable PLC input.
2. Check 2: With the beam blocked, expect the interface indication and PLC input to change once, without unexplained flicker.
3. Check 3: Run calibration at 100% feed override. Expect completion and updated calibration data without an axis-table message.
4. Check 4: Measure length and diameter separately for the first-row test tool. Expect a controlled approach, beam crossing, spindle response, and a recorded result without 160-00AE.
5. Check 5: Repeat the identical calls for a populated non-first-row tool. Expect both results to be written to that selected tool record; failure only here means the indexing or cycle-data correction is incomplete.

Frequently asked questions