Setting Temperature with Other NTCs

Overview

While the TEC controller is optimized for the NTCAFLEX05103HH sensor, you can use other 10kΩ NTC thermistors by calculating the appropriate potentiometer resistance values.

Calculation Procedure

Required Information

Obtain from your NTC datasheet:

R(T) curve - Resistance vs. Temperature characteristics
Beta value (B25/85 or similar)
Resistance at 25°C (should be 10kΩ for compatibility)

Calculating R_POT for Threshold Temperature

Formula

R_POT = R(NTC@TEMP) × 2.3791

Where:

R_POT = Resistance to set at TEMP ADJ measurement points
R(NTC@TEMP) = NTC resistance at your desired threshold temperature
2.3791 = Driver calibration factor

Calculation Steps

Select desired threshold temperature (e.g., 35°C)
Find NTC resistance at that temperature from datasheet
- Example: R(35°C) = 6.532 kΩ

Calculate required R_POT:

R_POT = 6.532 kΩ × 2.3791
R_POT = 15.537 kΩ

Set potentiometer:
- Measure at TEMP ADJ points
- Adjust to 15.537 kΩ

Calculating Hysteresis Temperature

Formula

R(NTC@HYST) = R_POT / 1.7034

Then find the temperature corresponding to this resistance in your NTC datasheet.

Calculation Steps

Use R_POT from above calculation

Calculate NTC resistance at hysteresis:

R(NTC@HYST) = 15.537 kΩ / 1.7034
R(NTC@HYST) = 9.120 kΩ

Find temperature in NTC datasheet
- Look up 9.120 kΩ in R(T) table
- Example: Corresponds to ~28°C
Result: Hysteresis temperature is 28°C

Complete Worked Example

Example: Vishay NTCLE100E3103JB0

Goal: Configure for 30°C nominal temperature

Step 1: Get NTC Characteristics

From datasheet:

R25 = 10 kΩ @ 25°C
B25/85 = 3977 K
R(30°C) = 8.059 kΩ (from datasheet table)

Step 2: Calculate R_POT

R_POT = R(30°C) × 2.3791
R_POT = 8.059 kΩ × 2.3791
R_POT = 19.169 kΩ

Step 3: Set Potentiometer

Disconnect power
Disconnect NTC
Measure at TEMP ADJ
Adjust to 19.169 kΩ

Step 4: Calculate Hysteresis

R(NTC@HYST) = 19.169 kΩ / 1.7034
R(NTC@HYST) = 11.254 kΩ

Step 5: Find Hysteresis Temperature

From NTC datasheet:

11.254 kΩ corresponds to approximately 22°C

Step 6: Calculate Threshold

The threshold temperature is approximately:

Nominal: 30°C
Hysteresis: 22°C
Spread: 8°C

For this NTC, the threshold would be approximately:

Threshold ≈ Nominal + (Nominal - Hysteresis)
Threshold ≈ 30°C + 8°C = 38°C

Result Summary

Configuration Results:
├─ Nominal Temperature:      30°C (TEC target)
├─ Hysteresis Temperature:   22°C (re-enable point)
├─ Threshold Temperature:    38°C (shutdown)
├─ Temperature Span:         8°C
└─ R_POT Setting:           19.169 kΩ

Alternative Calculation Using Beta

If only Beta value is available, calculate R(T):

Beta Formula

R(T) = R25 × exp(B × (1/T - 1/T25))

Where:

T = Temperature in Kelvin (°C + 273.15)
T25 = 298.15 K (25°C)
B = Beta value (e.g., 3977 K)
R25 = 10,000 Ω (10 kΩ @ 25°C)

Example Calculation

Find R(30°C) for NTC with B=3977K:

T = 30 + 273.15 = 303.15 K
T25 = 298.15 K
B = 3977 K
R25 = 10,000 Ω

R(30°C) = 10,000 × exp(3977 × (1/303.15 - 1/298.15))
R(30°C) = 10,000 × exp(3977 × (-0.0000537))
R(30°C) = 10,000 × exp(-0.2136)
R(30°C) = 10,000 × 0.8076
R(30°C) = 8,076 Ω ≈ 8.076 kΩ

Then use in R_POT calculation:

R_POT = 8.076 kΩ × 2.3791 = 19.210 kΩ

Setup Procedure

Complete Installation Steps

Disconnect power and NTC
Calculate R_POT using formulas above
Measure and adjust:
- Set multimeter to Ω mode
- Measure at TEMP ADJ points
- Adjust TEMP potentiometer to calculated R_POT
Solder NTC to connecting cables
- ✅ Polarity is NOT relevant
- Use heat-shrink tubing
- Keep wires as short as practical
Connect power supply
Test and verify:
- Power up system
- Check TEMP LED (should be ON)
- Monitor TEC operation
- Verify temperature control
After successful test, connect NTC:
- Connect to NTC port
- Secure connection
- Verify TEMP LED ON

Temperature Characteristics

Understanding Temperature Spread

The temperature difference between nominal and threshold depends on:

NTC Beta value
NTC R(T) curve characteristics
Driver calibration factors

Typical spreads: 5-10°C

NTC Beta	Approximate Spread
3400-3500 K	9-11°C
3800-4000 K	7-9°C
4200-4500 K	6-8°C

Higher Beta values generally give tighter temperature spans.

Compatible NTC Types

Example 10kΩ NTCs

Manufacturer	Part Number	B25/85 (K)	Notes
Murata	NXFT15XH103FA2B	3380	Wide span
Vishay	NTCLE100E3103JB0	3977	Good accuracy
TDK	B57164K0103J	3964	Standard type
Semitec	103AT-11	3435	Popular choice
Panasonic	ERT-J1VR103J	3950	High stability

Important Considerations

Temperature Difference Fixed by NTC

NTC Mounting

Optimal mounting:

Direct contact with laser package
Thermal paste for good coupling
Secure mechanical mounting
Protected from damage
Short wire runs

Thermal Contact Quality

Contact Method	Response Time	Accuracy	Suitability
Thermal paste	Fast	±1-2°C	Best
Thermal adhesive	Medium	±2-3°C	Good
Mechanical contact	Slow	±3-5°C	Acceptable
Air gap	Very slow	±5-10°C	Poor

Verification

After Setup Testing

Power up without laser enabled
Verify TEC operation:
- If ambient > nominal: TEC should activate
- If ambient < nominal: TEC should be off
- Monitor TEC LED
Test temperature control:
- Allow system to stabilize
- Measure actual temperature (if possible)
- Verify close to nominal setpoint
Test threshold:
- Carefully apply gentle heat
- Verify shutdown occurs at expected temperature
- Allow cooling
- Verify hysteresis temperature

Troubleshooting Custom NTC Setup

Temperature Not As Expected

Possible Causes:

Calculation error
Wrong NTC datasheet value
Beta value inaccurate

Solutions:

Double-check calculations
Verify datasheet R(T) values
Use actual R(T) table instead of Beta approximation

Temperature Spread Wrong

Cause: NTC characteristics different than expected

Solution:

Measure actual threshold and hysteresis
Document actual values
May need different NTC if spread unsuitable

Poor Temperature Stability

Possible Causes:

NTC too far from laser
Poor thermal contact
Wrong Beta value used

Solutions:

Improve NTC mounting
Verify thermal contact quality
Recalculate with correct Beta

TEC Behavior Erratic

Possible Causes:

Wrong R_POT calculation
NTC tolerance too large
Thermal feedback issues

Solutions:

Verify calculations
Use higher tolerance NTC (±1% preferred)
Improve thermal design

Documentation Template

Record Your Configuration

NTC Configuration Record
========================

Date: ______________
Configured by: ______________

NTC Specifications:
├─ Manufacturer: ______________
├─ Part Number: ______________
├─ R25: 10 kΩ @ 25°C
└─ Beta (B25/85): ________ K

Temperature Settings:
├─ Target Nominal: ______°C
├─ Calculated R_POT: ________ kΩ
├─ Hysteresis Temp: ______°C
└─ Threshold Temp: ______°C

Verification Results:
├─ Actual Nominal: ______°C
├─ Actual Hysteresis: ______°C
├─ Actual Threshold: ______°C
└─ Temperature Stability: ±______°C

Notes:
_________________________________
_________________________________
_________________________________

Best Practices

For Successful Custom NTC Implementation

✅ Use high-quality 10kΩ NTC (±1% tolerance)
✅ Get complete datasheet with R(T) table
✅ Double-check all calculations
✅ Verify Beta value is for B25/85
✅ Test thoroughly before final installation
✅ Document all settings
✅ Mount NTC with good thermal contact
✅ Keep wires short
✅ Protect NTC from mechanical damage
✅ Monitor initial operation closely