Unit 1 — Theory of Operation
TM-CAL-007 — Open Handout TM Chapter: Chapter 2 ELOs: Understand how the reference standard generates or maintains its reference value; identify key specifications Estimated time: 20 minutes
Step 1: Read the TM
Open TM-CAL-007. Read Chapter 2 — Theory of Operation completely.
Then come back here.
Chapter 2 Content
2-1. TEMPERATURE-COMPENSATED ZENER
Zener diodes exhibit a negative temperature coefficient (TC) below approximately 5.6 V and a positive TC above 5.6 V. At ~5.6 V zener voltage, TC ≈ 0. The 1N829 and LM336 are designed to operate at this compensation point.
A forward-biased diode (TC ≈ −2 mV/°C) in series with a 6.2 V zener (TC ≈ +2 mV/°C) achieves near-zero overall TC. The LM336 IC integrates this compensation internally.
| Device | Voltage | TC | Accuracy | Notes |
|---|---|---|---|---|
| LM336-2.5 | 2.5 V | <20 ppm/°C | ±1% | Adjustable with ext R |
| LM385-2.5 | 2.5 V | <50 ppm/°C | ±1% | Micropower |
| 1N829 | 6.2 V | <10 ppm/°C | ±0.5% | Hermetic zener |
| 1N5234 | 6.2 V | <100 ppm/°C | ±5% | General purpose |
2-2. RESISTOR DIVIDER
A precision resistor divider derives lower voltages from the master reference. Use 0.1% tolerance resistors for <0.2% division error.
Why Theory Matters for Calibration
You cannot calibrate what you do not understand. Theory tells you: - What the instrument or standard is supposed to do — so you recognize when it is not doing it - What the sources of error are — so you know which ones your calibration procedure addresses - What the limits of the calibration are — so you know when to stop and call it good
If a calibration measurement produces a surprising result, theory is where you look first.
Self-Check Questions
SC1-1. In one sentence, state the operating principle of the ZENER + DIVIDER MULTI-VOLTAGE REFERENCE as described in Chapter 2.
SC1-2. What does Chapter 2 identify as the primary source(s) of measurement error or uncertainty?
SC1-3. What key specification(s) (accuracy, range, resolution) does the TM state for this standard?
SC1-4. What safety precaution does §1-3 specify? State it exactly.
SC1-5. What references does §1-2 cite? List at least two.
Answer Key
SC1-1. See TM §2-1. Compare your sentence to the first substantive paragraph of Chapter 2.
SC1-2. See Chapter 2. Look for language about error sources, uncertainty, drift, or limiting factors.
SC1-3. See Chapter 2. Look for numbers with units: %, ppm, Hz, Ω, dB.
SC1-4. See TM §1-3. Copy the safety text exactly.
SC1-5. See TM §1-2. The references list is there.
Checkpoint
Before proceeding, state without looking: - The operating principle of the ZENER + DIVIDER MULTI-VOLTAGE REFERENCE - The primary error source(s) - At least one key specification with its value
→ Proceed to Unit 2