# MF51 Series Glass-Encapsulated NTC Thermistors

> Glass-encapsulated leaded NTC thermistors for temperature measurement from −20 °C to +250 °C. Three sizes with 1.2–2.0 mm body diameter; thermal time constant 2–11 s in static air.

- Series code: MF51
- Product line: [Thermistors (NTC / PTC)](https://www.songtian-ste.com/en/products/thermistors/) › NTC thermistors for temperature sensing and compensation
- Part numbers: Part-number list on request
- Page: https://www.songtian-ste.com/en/products/ntc-thermistors/mf51/
- Chinese version: https://www.songtian-ste.com/zh/products/ntc-thermistors/mf51/
- [Ask AI about this series](https://www.songtian-ste.com/en/products/ntc-thermistors/mf51/?ask=Help%20me%20choose%20a%20part%20from%20the%20STE%20MF51%20series.)

## Key specifications

| Parameter | Value |
| --- | --- |
| Operating temperature | −20 °C to +250 °C |
| Thermal time constant, static air | 2–11 s |
| R25 tolerance | ±1% to ±10% |
| B-value tolerance | ±1% / ±2% |
| Body diameter | 1.2 / 1.6 / 2.0 mm |
| Rated power | ≤15 to ≤50 mW |

## Engineering details

### Overview

Glass-encapsulated leaded NTC thermistors for temperature measurement from −20 °C to +250 °C. Three constructions, MF51-A, -B and -C, with body diameters of 2.0, 1.6 and 1.2 mm; thermal time constant 2–11 s in static air and 0.18–1.1 s in flowing oil. R25 tolerance ±1% to ±10%, B-value tolerance ±1% or ±2%.

#### Series features

- Glass-encapsulated sensing element in 1.2, 1.6 and 2.0 mm body diameters
- Thermal time constant specified in static air and flowing oil for each construction (A, B, C)
- Dissipation constant in static air and rated power specified per construction
- R25 tolerance ±1% to ±10%; B-value tolerance ±1% or ±2%
- Bulk packed, 65 mm leads; operating temperature −20 °C to +250 °C

#### Typical applications

- Temperature feedback in air-conditioning and heating
- Liquid-temperature sensing
- Electronic thermometers and precision instruments
- Temperature control in household appliances and industrial equipment
- High-temperature or humid environments, after seal and drift validation in the application

### Specifications

|   |   |
| --- | --- |
| Function | Leaded NTC thermistor for temperature measurement; zero-power resistance decreases as the temperature of the sensing element rises |
| Construction | Glass-encapsulated NTC sensing element with leads |
| Constructions | MF51-A · MF51-B · MF51-C |
| Operating temperature | −20 °C to +250 °C |
| High-temperature use | Power derating, lead and seal temperature limits, life and drift limits across −20 °C to +250 °C on request. |
| Zero-power resistance | DC resistance at temperature t, measured at a power low enough that any further reduction changes the resistance by less than 0.1% |
| R25 code examples | 102 = 1 kΩ · 103 = 10 kΩ · 104 = 100 kΩ · 105 = 1,000 kΩ |
| R25 values | Available R25 and B-value combinations on request. |
| R25 tolerance codes | F ±1% · G ±2% · H ±3% · J ±5% · K ±10% |
| B-value definition | B = ln(R1/R2) / (1/T1 − 1/T2) |
| B-value reference temperatures | T1 = 298.15 K (25 °C); T2 = 323.15 K (50 °C) or 358.15 K (85 °C) |
| B-value tolerance codes | F ±1% · G ±2% |
| Temperature accuracy | R25 and B tolerances do not state a ±°C accuracy. Calculate the temperature error from the R/T table of the selected part number. |
| Dimensions, MF51-A | D 2.0 ±0.2 · H 3.8 ±0.5 · L 65 ±2.5 · lead Ø d 0.30 ±0.02 mm |
| Dimensions, MF51-B | D 1.6 ±0.2 · H 3.2 ±0.5 · L 65 ±2.5 · lead Ø d 0.25 ±0.02 mm |
| Dimensions, MF51-C | D 1.2 ±0.2 · H 2.4 ±0.5 · L 65 ±2.5 · lead Ø d 0.20 ±0.02 mm |
| Thermal time constant, MF51-A | 10–11 s in static air · 0.9–1.1 s in flowing oil |
| Thermal time constant, MF51-B | 4–5 s in static air · 0.3–0.4 s in flowing oil |
| Thermal time constant, MF51-C | 2–3 s in static air · 0.18–0.24 s in flowing oil |
| Thermal time constant, definition | Time to reach 63.2% of the change from initial to final temperature, under zero-power conditions |
| Dissipation constant, MF51-A | 1.2–1.3 mW/°C in static air |
| Dissipation constant, MF51-B | 0.7–0.8 mW/°C in static air |
| Dissipation constant, MF51-C | 0.4–0.5 mW/°C in static air |
| Rated power | MF51-A ≤50 mW · MF51-B ≤35 mW · MF51-C ≤15 mW |
| Terminal option | 0 = without terminal · P = with terminal |
| Lead length | Standard 65 ±2.5 mm; coded in the last four characters of the part number |
| Hand soldering and rework | 300 °C max. · 3 s max. · solder point at least 2 mm from the glass body |
| Packing | Bulk |
| Storage | ≤35 °C · ≤70% RH · 12 months · keep the original package closed and reseal after opening; protect lead solderability from corrosive atmospheres |
| Environmental compliance | RoHS and REACH compliant; halogen status and material declarations on request |
| Further data | On request: resistance–temperature (R/T) table of each part number · terminal type and drawing · lead-length code table · max. sensing current and voltage, allowed self-heating error and power derating versus temperature · max. working voltage, dielectric withstand and insulation resistance · lead alloy, plating and solderability finish · glass-seal hermeticity, insulation-resistance and moisture-ingress data · wave or reflow soldering conditions, lead-forming radius, cleaning and potting compatibility · endurance, high- and low-temperature storage, thermal-shock, humidity, vibration, lead-strength and solderability results |
| Automotive use | No AEC-Q200 qualification is specified for this series |

### Variants

Ranges by dielectric, package and lead style within this series.

| Variant | Body dimensions | R25 / B value | Thermal time constant / dissipation constant / rated power | Lead / land pattern | Notes |
| --- | --- | --- | --- | --- | --- |
| MF51-A | D 2.0 × H 3.8 mm · L 65 mm · d 0.30 mm (nom.) | Per part number | Air 10–11 s · oil 0.9–1.1 s · 1.2–1.3 mW/°C · ≤50 mW | Leaded glass body · terminal option 0 or P | Largest body and highest rated power. Validate high-temperature construction, self-heating and response in the medium. |
| MF51-B | D 1.6 × H 3.2 mm · L 65 mm · d 0.25 mm (nom.) | Per part number | Air 4–5 s · oil 0.3–0.4 s · 0.7–0.8 mW/°C · ≤35 mW | Leaded glass body · terminal option 0 or P | Intermediate size and response, for general liquid or air sensing. |
| MF51-C | D 1.2 × H 2.4 mm · L 65 mm · d 0.20 mm (nom.) | Per part number | Air 2–3 s · oil 0.18–0.24 s · 0.4–0.5 mW/°C · ≤15 mW | Leaded glass body · terminal option 0 or P | Smallest and fastest construction. Protect the fine leads and limit the excitation. |

### Selection guide

Start with the temperature range, system accuracy and response in the actual medium. Then select R25 and B value from the R/T table of the selected part number, choose the A, B or C construction, limit self-heating and validate the glass-to-lead interface.

1. **Define temperature, accuracy and mission profile**
   Set sensor and ambient extremes, required ±°C error, response, drift, calibration, life and the safety consequence of a sensing error. For use near +250 °C, obtain construction and life data before design-in.
2. **Select R25, B value and R/T data**
   Choose R25 for the divider and ADC range and B25/50 or B25/85. Use the R/T table and tolerance band of the selected part number.
3. **Select A, B or C from the thermal path**
   Use C for the smallest body and fastest response, A for the highest rated power, or B between them. Validate response in the actual fluid, airflow, contact and mounting condition.
4. **Limit self-heating and electrical stress**
   Calculate divider power at every resistance and supply tolerance. Keep excitation within the error budget, using the max. voltage and current, power derating and allowed self-heating of the selected part.
5. **Specify construction, process and qualification**
   Specify glass seal and lead materials, terminal and lead drawing, soldering and strain relief, packing, environmental declarations and qualification for each part number.

### Design notes

#### +250 °C is not a lifetime rating

At the max. mission-profile temperature, define the construction (A, B or C), exposure time, duty, atmosphere, lead and seal temperature and the resistance-drift limit.

#### R25 tolerance is not full-range accuracy

System error includes R25 and curve tolerance, ADC, reference and divider error, self-heating, thermal gradients, calibration and aging. Obtain the R/T tolerance band at every critical temperature.

#### Validate response in the actual medium

Response in oil depends on oil type and flow. Contact, potting, immersion depth, airflow and enclosure geometry can dominate the response. Correlate the finished assembly against reference thermometry.

#### Keep excitation within the error budget

The C construction has the lowest dissipation constant and rated power. Use pulsed or lower-current measurement where needed and verify max. supply and resistance corners against the self-heating limits.

#### Protect the glass-to-lead interface

Avoid bending or clamping near the body, differential-expansion stress, unsupported vibration and uncontrolled potting cure. Use a defined forming radius, strain relief and compatible sealing and cleaning processes.

### Part numbering

Example ordering code. Not every combination is available.

`MT · 51A · 103 · F · 3950 · F · 0 · 0000`

| Code | Meaning |
| --- | --- |
| MT | Temperature-sensing NTC prefix |
| 51A | Construction: 51A; 51B and 51C for the other sizes |
| 103 | R25: 103 = 10 kΩ; 102 = 1 kΩ, 104 = 100 kΩ, 105 = 1 MΩ |
| F | R25 tolerance: F = ±1%; G ±2%, H ±3%, J ±5%, K ±10% |
| 3950 | Nominal B value in K; available values and B25/50 or B25/85 basis per part number |
| F | B-value tolerance: F = ±1%; G = ±2% |
| 0 | Terminal: 0 = without terminal; P = with terminal |
| 0000 | Lead length; code table on request |

## Datasheets & approval documents

- [Technical document: MF51 series glass-encapsulated NTC thermistors for temperature sensing](https://www.songtian-ste.com/documents/source-cn/%E8%B4%9F%E6%B8%A9%E5%BA%A6%E7%B3%BB%E6%95%B0%E7%83%AD%E6%95%8F%E7%94%B5%E9%98%BB%E5%99%A8-MF51%E7%8E%BB%E5%B0%81%E6%B5%8B%E6%B8%A9%E5%9E%8B%E7%B3%BB%E5%88%97.pdf) — PDF · Chinese · 285 KB

## More in NTC sensing thermistors

- [SMD Sensing NTC · SMD NTC Thermistors for Temperature Measurement](https://www.songtian-ste.com/en/products/smd-thermistors/smd-sensing/)
- [MF51 Special NTC Temperature Sensors for Electronic Thermometers](https://www.songtian-ste.com/en/products/ntc-thermistors/mf51-electronic-thermometer/)
- [MF52 Series Bead-Type Precision NTC Temperature Sensors](https://www.songtian-ste.com/en/products/ntc-thermistors/mf52/)
- [MF58 Series Glass-Encapsulated NTC Thermistors (Diode Type)](https://www.songtian-ste.com/en/products/ntc-thermistors/mf58/)
- [MF59 Series Glass-Encapsulated Chip NTC Thermistors](https://www.songtian-ste.com/en/products/ntc-thermistors/mf59/)
- [CWF Series Precision NTC Temperature Sensors](https://www.songtian-ste.com/en/products/ntc-thermistors/cwf/)