Unit 5 — Calibration and Verification

TM-GEAR-004 — Open Handout TM Chapters: Chapter 6, Chapter 7 ELOs: Calibrate the BATTERY MANAGEMENT SYSTEM (BMS) — LiFePO4 AND LI-ION; verify performance against acceptance criteria; complete calibration log Estimated time: 45 minutes (actual lab work required)

Step 1: Read the TM

Open TM-GEAR-004. Read Chapter 6 — Calibration and Chapter 7 — Verification and Acceptance completely.

Then come back here.

Chapter 6 — Calibration Content

1. Calibrate cell voltage offsets: measure each cell with a precision DMM (Fluke 15B+). Compare to BQ76920 I2C readings. Enter offset corrections in firmware NVS (ESP32 Preferences library).
2. Calibrate current sense: apply a known load (resistive, measured with the calibrated DMM). Adjust firmware current-sense gain constant until displayed current matches measured.
3. Calibrate SOC: fully charge pack to 14.4V. Reset Coulomb counter to 100%. Discharge completely to 10.0V. Record Ah removed. Compare to cell rated capacity. Adjust C_nominal in firmware.

Chapter 7 — Verification Content

1. All cell voltages within 20 mV of each other at rest (balanced).
2. OV protection: charge one cell to 3.70V (using external bench supply on sense pins). Verify BQ76920 opens CHG FET within 2 seconds.
3. UV protection: discharge to 9.8V. Verify DSG FET opens within 1 second.
4. Overcurrent: apply a momentary 60 A load for 100 ms. Verify DSG FET opens (BQ76920 OCD detection).
5. Log: date, cell batch numbers, initial balance spread (mV), OV trip voltage, UV trip voltage, OCD trip current, measured capacity (Ah), operator.

Calibration vs. Verification — Distinction

Calibration (Chapter 6): active adjustments to bring the component within specification. You are permitted to adjust, tweak, and repeat until the criterion is met.

Verification (Chapter 7): independent confirmation that the calibration succeeded. No adjustments are permitted during verification. If a verification check fails, you return to Chapter 6, not to Chapter 7.

Acceptance Criterion

A criterion found in Chapter 6: 100%. Confirm the exact criterion in the TM.

Write the exact criterion from the TM here before you start the lab:

Lab Checklist

Work through each item in sequence. Do not skip steps.

• [ ] All required equipment gathered and ready
• [ ] Equipment warmed up per TM requirements
• [ ] All Chapter 4 setup steps verified complete
• [ ] Chapter 6 calibration performed (all steps)
• [ ] Calibration criterion met (recorded below)
• [ ] Chapter 7 verification performed (all steps, no adjustments)
• [ ] All verification criteria passed
• [ ] Calibration log entry completed

Calibration Log Entry

• [ ] Date
• [ ] Equipment used
• [ ] Measurements taken
• [ ] Results vs. criteria
• [ ] Operator name

Record your results:

Self-Check Questions

SC5-1. What is the acceptance criterion for this calibration (from Chapter 7)?

SC5-2. During verification, one reading fails. What is the correct action per the TM?

SC5-3. List the items required in a calibration log entry per Chapter 7.

SC5-4. What is the difference between calibration and verification in this context?

SC5-5. If the component passes all Chapter 7 checks, what does that tell you about its current state?

Answer Key

SC5-1. See Chapter 7. The criterion is stated as a specific value with units.

SC5-2. Stop verification. Return to Chapter 6 and re-calibrate. Diagnose the cause before re-adjusting.

SC5-3. See Chapter 7, last numbered step. The log items are listed there.

SC5-4. Calibration allows adjustments; verification does not. Verification is independent confirmation.

SC5-5. It tells you the component is performing within its specified parameters at this time. It does not tell you how long it will remain in calibration — periodic re-verification is required.

Checkpoint

You are ready for the final assessment when you can: - [ ] State the acceptance criterion from memory - [ ] State the difference between calibration and verification - [ ] State the required log items from memory

→ Proceed to Final Assessment