PCB Design for Motor Monitoring
Now help me finish the connections
Thought for 5 sec
I’ll finish the schematic connections by first reading the current component pins and uploaded measurement/sensor/connector data, then I’ll wire the sensor, protection, isolation, Dspace connector, and test-point nets and run review checks.
Worked for 6 mins 4 sec
Finished the schematic connections for the current measurement interface: LV25-P voltage channel, LA25-P current secondary channel, ±15 V isolated sensor supplies, AGND return, burden resistors, TVS output protection, temporary dSPACE output connector, and labeled TP1/TP2 test points.
I updated the measurement/safety project file: DFIG Measurement Interface — Project Requirements. ERC now reports clean; DRC airwires remain because the board has not been placed/routed yet.
Remaining before layout/manufacture: replace temporary J2 with the exact TE 1761028-5 100-pin dSPACE connector when available, resolve the current-sensor primary/turns footprint representation, then proceed to placement and routing after your confirmation.
Add exact J2
Resolve U2 footprint
Run ERC/DRC
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DFIG Measurement Interface — Project Requirements
Purpose
Design a PCB/interface circuit for measuring Wound Rotor Induction Motor (WRIM/DFIG) terminal quantities from the stator and slip-ring/rotor terminal box, condition those measurements through voltage and current sensors, and feed safe analogue signals into the dSPACE 1104/CLP1104 interface.
Clarified Measurement Ranges to Use
Only technically sensible ranges from the clarification report are included here. Values that depend on unverified machine nameplates are treated as target/design ranges until confirmed in the lab.
Voltage Measurements
Table
| Measurement point | Design range to support | Basis / note |
|---|---|---|
| Stator line-to-line voltage | 380 V RMS nominal, design for 456 V RMS with 20% margin | Use for WRIM stator/variac supply measurements. |
| Rotor/slip-ring voltage | Approx. 100 V RMS nominal, design for 120 V RMS with 20% margin | Use for rotor/slip terminal voltage measurements. |
| DC-link / DC supply voltage, if included | 0–300 V DC for present hardware tests; allow up to 600 V DC as future design reference if converter hardware is added | 300 V is the current practical hardware envelope; 600 V is a thesis/reference design level, not an immediate operating requirement unless future converter tests require it. |
Current Measurements
Table
| Measurement point | Design range to support | Basis / note |
|---|---|---|
| WRIM stator current | Practical expected range 4–6 A RMS; design sensor/protection around this until nameplate FLC is verified | Matches the LRD10 overload adjustment range and expected 2.2 kW, 380/400 V lab machine current. |
| Rotor/slip current | Use same initial measurement envelope as motor current: 4–6 A RMS practical target; sensor range should tolerate at least ±7.2 A when using 5 primary turns on LA 25-NP | Final value must be confirmed from motor nameplate/test plan. |
| Wider current sensor capability | LA 25-NP supports ±36 A-turns; with 5 primary turns, effective range is ±7.2 A | 5 turns improves sensitivity for 4–6 A motor-current measurements. |
Sensor Scaling Requirements
LEM LV 25-P Voltage Sensor
- Supply rail: ±12 V to ±15 V; use ±15 V if consistent with the rest of the analogue front end.
- Primary nominal RMS current: 10 mA.
- Primary measuring range: ±14 mA.
- Use an external high-voltage primary resistor chain sized for both voltage rating and power dissipation.
- With 100 kΩ primary resistance:
- 456 V gives 4.56 mA primary current.
- 120 V gives 1.2 mA primary current.
- 300 V DC gives 3 mA primary current.
- 600 V DC gives 6 mA primary current.
- These currents remain below the ±14 mA LV 25-P primary measurement limit.
- Current schematic channel: J1 pin 1 → R1 100 kΩ HV resistor-chain placeholder → U1 +HV; J1 pin 2 → U1 -HV.
- Secondary side: U1 M → R2 100 Ω burden to AGND; this creates V_MEAS_OUT. At 25 mA nominal secondary current, the nominal output is 2.5 V.
LEM LA 25-NP / LA 25-P Current Sensor
- Supply rail: ±15 V.
- Nominal primary current: 25 A-turns.
- Measuring range: ±36 A-turns.
- For the expected 4–6 A motor-current range, use 5 primary turns where practical:
- 4 A → 20 A-turns.
- 6 A → 30 A-turns.
- Effective measuring range becomes about ±7.2 A.
- Current schematic secondary side: U2 M → R3 100 Ω burden to AGND; this creates I_MEAS_OUT. At 25 mA nominal secondary current, the nominal output is 2.5 V.
- Important limitation: the current Flux symbol currently exposes only M, +, and - secondary pins for U2. The LA 25-NP datasheet primary terminals/turn selections must still be represented mechanically/electrically in the final footprint or by replacing the symbol with a complete LA 25-NP part before layout/manufacture.
Current Schematic Connection Map
Table
| Net | Connected items | Function |
|---|---|---|
| +15V_ISO | J3 pin 1, U1 +, U2 +, C1, C3 | Isolated positive secondary supply for LEM sensors. |
| -15V_ISO | J4 pin 1, U1 -, U2 -, C2, C4 | Isolated negative secondary supply for LEM sensors. |
| AGND | J3 pin 2, J4 pin 2, J2 pin 2, R2/R3 returns, D1 A, C1–C4 returns | Isolated analogue ground / dSPACE measurement return. |
| VOLT_HV_POS | J1 pin 1, R1 pin 1 | Hazardous motor-side voltage sense input before high-voltage resistor chain. |
| VOLT_HV_POS_SCALED | R1 pin 2, U1 +HV | Current-limited LV25-P primary input. |
| VOLT_HV_NEG | J1 pin 2, U1 -HV | Hazardous motor-side voltage sense return. |
| V_MEAS_OUT | U1 M, R2 pin 1, TP1, D1 protected channel, J2 pin 1 | Low-voltage voltage-measurement output to dSPACE. |
| I_MEAS_OUT | U2 M, R3 pin 1, TP2, D1 protected channel | Low-voltage current-measurement output test channel. |
dSPACE / D-sub Interface Requirements
- Feed only conditioned, low-voltage analogue measurement signals into the dSPACE 1104/CLP1104 interface.
- Keep all outputs to dSPACE within its allowed analogue input range; target a conservative ±10 V maximum interface range unless a more restrictive channel limit is confirmed from the dSPACE datasheet.
- Use the TE Connectivity 1761028-5 100-position D-sub only for low-voltage signals, logic, interlocks, and dSPACE interface wiring.
- Do not route stator, rotor, DC-machine armature, variac, or converter power current through the D-sub connector.
- Use shielding, grounding strategy, and physical separation between high-power motor wiring and low-level measurement signals.
- Current schematic note: the exact TE 1761028-5 part was not available in the Flux library during this pass, so J2 is a temporary 2-position low-voltage dSPACE output connector. Replace J2 with the exact 100-position D-sub connector once the part/footprint is available, then map V_MEAS_OUT, I_MEAS_OUT, and AGND to the chosen dSPACE analogue input pins.
Protection and Isolation Requirements
- Include input protection on motor terminal measurement inputs before/around the sensor front end.
- Maintain galvanic isolation between hazardous motor terminals and the low-voltage/dSPACE side through the selected LEM voltage/current transducers.
- High-voltage resistor chains for stator/rotor voltage measurement must be rated for the maximum design voltage and appropriate power dissipation.
- Add filtering and clamp/overvoltage protection on conditioned analogue outputs before the dSPACE connector.
- D1 provides TVS/ESD clamping for the low-voltage analogue outputs to AGND; unused TVS channels are marked no-connect.
- C1–C4 provide local 100 nF bypassing on the ±15 V isolated sensor supplies.
- Protection hardware for the motor path remains subject to nameplate verification:
- LRD10 overload setting must match actual WRIM full-load current.
- If the actual machine current is outside 4–6 A, the overload relay range must be changed.
Safety Assumptions
- The ±15 V supply entering J3/J4 is an isolated SELV/PELV laboratory supply with no direct connection to the motor primary side except through the transducers.
- The PCB is a measurement/interface board, not a power-distribution board.
- Motor terminal wiring connected to J1 and the current transducer primary path is hazardous and must be enclosed, strain-relieved, fused/protected upstream, and separated physically from low-voltage/dSPACE wiring.
- The R1 100 kΩ item is a schematic placeholder for a certified high-voltage resistor chain. In the PCB layout this should be implemented as multiple series resistors with adequate voltage rating, creepage/clearance, pulse energy rating, and power dissipation.
- Final commissioning requires WRIM, DC machine, variac, supply, and protection nameplate verification before energisation.
Explicitly Excluded / Not Yet Final
- Do not treat the DC converter as a full DFIG rotor-side/grid-side AC converter unless suitable inverter/converter hardware is confirmed.
- Do not finalize protection settings until WRIM, DC machine, variac, and supply nameplates are verified.
- Do not route high-power motor conductors through the PCB D-sub interface.
- Do not proceed to PCB layout/manufacture until the exact dSPACE connector footprint and the complete current-sensor primary pin representation are resolved.
Purpose
Clarified Measurement Ranges to Use
Voltage Measurements
Current Measurements
Sensor Scaling Requirements
LEM LV 25-P Voltage Sensor
LEM LA 25-NP / LA 25-P Current Sensor
Current Schematic Connection Map
dSPACE / D-sub Interface Requirements
Protection and Isolation Requirements
Safety Assumptions
Explicitly Excluded / Not Yet Final
