MR-J4-A analog traces: tenfold scaling differences and the 5 V zero point

If an analog trace falls from 4 V before repair to 0.4 V afterward, has following error fallen by 90%? Different monitor scales can invalidate that conclusion. Based on Mitsubishi Electric SH(NA)030107ENG-V (November 2025), this article covers motor-side droop monitoring with rotary servo motors in semi-closed-loop position control. It interprets existing records, rather than providing setup or trial-operation instructions.

1. Identify the internal quantity represented by voltage

MO1 and MO2 are analog monitor outputs selected by PC14 and PC15 respectively. Appendix 7.2 says their factory selections are motor speed and torque. A trace labeled “channel 1” is therefore not automatically position deviation. Read the complete effective parameter values at the time of recording and decode the rightmost two hexadecimal digits. Both __06 and __07 select motor-side droop pulses, but their scales differ. Underscores represent the other digits; this is not an instruction to overwrite a parameter.

The semi-closed-loop diagram in Appendix 7.3.1 places droop pulses at the comparison between position command and position feedback. This is not an independent measurement at the machine table or a value already expressed in millimeters. Pulses here are motor encoder pulses. Converting them into mechanical travel also requires verified encoder and transmission data for the machine. Appendix 7.2 notes that these droop outputs cannot be used in speed or torque control.

2. Separate the amplifier models before applying a scale

Manual model group	Selection	Scale without additional offset
MR-J4-_A_(-RJ), 100 W or more	__06	±10 V for ±100 pulses; zero deviation is 0 V
Same group	__07	±10 V for ±1000 pulses; zero deviation is 0 V
MR-J4-03A6(-RJ)	__06	5 V ±4 V for ±100 pulses; zero deviation is 5 V
Same group	__07	5 V ±4 V for ±1000 pulses; zero deviation is 5 V

Sources are §5.2.3, Tables 5.8 and 5.9 (5-45 to 5-46), and Appendix 7.2 (App.-25 and App.-27 to App.-28). The MR-J4-03A6 5 V center is part of its specified scale, not evidence of output-circuit drift. Do not transfer these ratios directly to MR-J4-B, MR-J5, linear motors or fully closed-loop load-side monitoring.

3. Hypothetical calculation: a smaller trace with unchanged deviation

This is a teaching example, not a field case, measured result or test to reproduce. Assume a 100 W-or-above model, verified semi-closed-loop position control, zero offsets in both existing records, and no additional acquisition scaling, clipping or timing-alignment issue.

Record A uses __06 and reads +4 V: deviation is 4÷10×100=+40 encoder pulses. Record B uses __07 and reads +0.4 V: deviation is 0.4÷10×1000=+40 encoder pulses. Voltage amplitude has fallen tenfold, but the represented deviation has not decreased. Conversely, +4 V with __07 represents +400 pulses, not the +40 pulses represented by __06.

For a separate hypothetical MR-J4-03A6 record using __06 without additional offset, first subtract the 5 V center from a +5.8 V reading: (5.8−5)÷4×100=+20 pulses. Signs follow the manual’s monitor-direction convention; do not identify them with the machine X-axis directions without verification.

4. Offsets and acquisition can change the interpretation

PC39 is the MO1 offset and PC40 the MO2 offset, in mV. Section 5.2.3 (5-52) and Appendix 7.1 specify a range of −9999 to 9999 mV. Read and record existing values; that range is not a recommended adjustment. When offsets are nonzero, do not reuse the zero-offset formulas unchanged. Establish conversion using the effective offset and acquisition zero, gain and polarity. Do not change parameters merely to “zero” a curve and hide real deviation or the original monitoring configuration.

Also verify whether the recorded channel is MO1 or MO2, whether its reference is LG, whether the recorder has already converted the data, and whether channels share a time base. This means checking existing diagrams and records, not connecting probes live. A flat-topped trace beyond the recorder’s range suggests possible clipping; its plateau cannot reveal the actual deviation peak. Appendix 7 warns that analog output can be irregular at power-on, so an isolated startup spike does not establish a following fault.

5. Diagnostic decisions and handover

Only trace amplitude changes: convert each record using its own selection, model and offset, then compare the same motion phase in common units. A difference remains after conversion: examine existing command, speed, deviation and alarm records for evidence of a real tracking change. An analog trace alone does not justify replacing an amplifier or encoder. Model, parameters or acquisition scale are missing: report “quantitative comparison unavailable,” not “improved after repair.”

Preserve full amplifier and motor models, amplifier software version, control mode, complete PC14/PC15/PC39/PC40 values, recording time, channel names, units, acquisition gain and raw traces. The cited entries do not impose a single software-version threshold like some other functions. This does not establish identical behavior across all models and versions; verify the manual applicable to the actual equipment.

Safety limits: this article only interprets existing records that can be obtained safely. It does not authorize live cabinet access, wiring, parameter changes or trial motion. Zero analog monitor voltage does not prove a de-energized bus or absence of mechanical stored energy. Qualified personnel must follow the machine’s approved isolation and residual-energy verification procedure and Safety Instructions A-2.

Source: MR-J4-_A_(-RJ)/MR-J4-03A6(-RJ) Servo Amplifier Instruction Manual, SH(NA)030107ENG-V (November 2025, English original): §5.2.3, Tables 5.8/5.9, 5-45 to 5-46; PC39/PC40, 5-52; Appendices 7.1 to 7.3.1, App.-24 to App.-29; Safety Instructions A-2. All page references are printed numbers. Calculations and diagnostic decisions are editorial analysis, not manufacturer repair cases or prescribed tests.