Pt50 | GUILCOR SENSORS

Pt50
Temperature sensors

Pt50 temperature sensors offer a balanced combination of accuracy and improved signal level compared to low-resistance RTDs.

Maximum precision
+/- 0.15°K

Minimum temperature
-200°C

Maximum temperature
+600°C

Minimum dimensions
2x25x45

Response time
Fast

Self-heating
Weak

Price
High

Drift
Weak

What is a Pt50 sensor ?

The Pt50 is a platinum RTD sensor with a nominal resistance of 50 Ω at 0 °C.

It offers an ideal compromise between sensitivity, stability, and linearity, while generating a more comfortable measurement voltage than the Pt10.

Used in industrial systems, thermal control chains, and test benches, it combines platinum precision with better noise immunity.

Operating principle

Like other platinum sensors, the Pt50 follows the Callendar–Van Dusen equation :

R(T) = R0[(1+A⋅T+B⋅T²+C⋅(T-100)⋅T³]

with :

R_0 = 50 Ω
A = 3,9083 × 10⁻³
B = -5,775 × 10⁻⁷
C = −4,183×10−12 (pour T < 0 °C)

This relationship gives the Pt50 excellent linearity and high stability over the range of −200 °C to +600 °C.

Technical specifications

Parameter	Typical Value
Nominal resistance at 0 °C	50 Ω
Temperature coefficient (α)	0,00385 °C⁻¹
Measurement range	−200 °C to +600 °C
Linearity	Excellent
Element material	Platinium pur (99,99 %)
Typical measuring current	0,3 to 1 mA
Response time	< 0,4 s (Ø2 mm)
Long-term drift	< 0,05 °C/year

Wiring configuration

Type	Description	Precision
2-wire	Simple, but the cable resistance adds to the measurement.	⚠️ Average
3-wire	Partially compensates for parasitic resistance.	✅ Good
4-wire	Kelvin measurement: completely cancels line errors.	🏆 Excellent

Self-heating

The Pt50 generates negligible power even under 1 mA.

Self-heating remains below 0.05 °C, ensuring reliable measurements, even in isolated environments or with low air circulation.

Application areas

⚙️ Industrial process control

🌡️ Laboratory equipment temperature control

🔧 Embedded instrumentation

🧪 Calibration and thermal test benches

🏭 Measurement systems in harsh environments

Should I choose a Pt50 sensor ?

Strengths points

⚙️ Excellent technical compromise
→ Offers an ideal balance between resistance, precision, and sensitivity, perfectly suited for demanding industrial environments.
🧠 Easy to integrate
→ It's nominal resistance of 50 Ω produces a measurable voltage without extreme amplification, compatible with most standard measurement systems.
🧩 Long-term stability
→ Pure platinum ensures exceptional measurement reproducibility, even after several years of operation.

Weaknesses points

💸 Higher cost than nickel or copper
→ Platinum remains a noble material; therefore, the Pt50 is more expensive to purchase.
🔌 Requires careful wiring
→ Measurement errors increase with poor contacts or unshielded cables; a 3 or 4-wire setup is highly recommended.
🌡️ Limited sensitivity to small variations
→ Compared to a Cu10 or Cu50, the Pt50 shows a smaller resistance change per degree, making the detection of micro-temperature changes more complex.

Useful information

Here is some useful information about Pt50 sensors.

Table of ohmic values

	0°C	1°C	2°C	3°C	4°C	5°C	6°C	7°C	8°C	9°C
0°C	50	50,195	50,391	50,586	50,781	50,976	51,171	51,366	51,561	51,756
10°C	51,951	52,146	52,341	52,536	52,73	52,925	53,119	53,314	53,508	53,702
20°C	53,897	54,091	54,285	54,479	54,673	54,867	55,061	55,255	55,449	55,643
30°C	55,836	56,03	56,224	56,417	56,611	56,804	56,998	57,191	57,384	57,577
40°C	57,77	57,963	58,156	58,349	58,542	58,735	58,928	59,121	59,313	59,506
50°C	59,699	59,891	60,084	60,276	60,468	60,66	60,853	61,045	61,237	61,429
60°C	61,621	61,813	62,005	62,197	62,388	62,58	62,772	62,963	63,155	63,346
70°C	63,538	63,729	63,92	64,111	64,303	64,494	64,685	64,876	65,067	65,258
80°C	65,448	65,639	65,83	66,021	66,211	66,402	66,592	66,783	66,973	67,163
90°C	67,353	67,544	67,734	67,924	68,114	68,304	68,494	68,684	68,873	69,063
100°C	69,253	69,442	69,632	69,821	70,011	70,2	70,39	70,579	70,768	70,957
110°C	71,146	71,335	71,524	71,713	71,902	72,091	72,28	72,468	72,657	72,845
120°C	73,034	73,222	73,411	73,599	73,787	73,976	74,164	74,352	74,54	74,728
130°C	74,916	75,104	75,292	75,479	75,667	75,855	76,042	76,23	76,417	76,605
140°C	76,792	76,979	77,167	77,354	77,541	77,728	77,915	78,102	78,289	78,476
150°C	78,663	78,849	79,036	79,223	79,409	79,596	79,782	79,968	80,155	80,341
160°C	80,527	80,713	80,899	81,085	81,271	81,457	81,643	81,829	82,015	82,2
170°C	82,386	82,572	82,757	82,943	83,128	83,313	83,499	83,684	83,869	84,054
180°C	84,239	84,424	84,609	84,794	84,979	85,164	85,348	85,533	85,717	85,902
190°C	86,086	86,271	86,455	86,64	86,824	87,008	87,192	87,376	87,56	87,744
200°C	87,928	88,112	88,296	88,479	88,663	88,847	89,03	89,214	89,397	89,58
210°C	89,764	89,947	90,13	90,313	90,496	90,679	90,862	91,045	91,228	91,411
220°C	91,594	91,776	91,959	92,142	92,324	92,507	92,689	92,871	93,054	93,236
230°C	93,418	93,6	93,782	93,964	94,146	94,328	94,51	94,691	94,873	95,055
240°C	95,236	95,418	95,599	95,781	95,962	96,143	96,325	96,506	96,687	96,868
250°C	97,049	97,23	97,411	97,592	97,773	97,953	98,134	98,314	98,495	98,676
260°C	98,856	99,036	99,217	99,397	99,577	99,757	99,937	100,117	100,297	100,477
270°C	100,657	100,837	101,017	101,196	101,376	101,555	101,735	101,914	102,094	102,273
280°C	102,452	102,632	102,811	102,99	103,169	103,348	103,527	103,706	103,885	104,063
290°C	104,242	104,421	104,599	104,778	104,956	105,135	105,313	105,491	105,669	105,848
300°C	106,026	106,204	106,382	106,56	106,738	106,915	107,093	107,271	107,449	107,626
310°C	107,804	107,981	108,159	108,336	108,513	108,691	108,868	109,045	109,222	109,399
320°C	109,576	109,753	109,93	110,107	110,283	110,46	110,637	110,813	110,99	111,166
330°C	111,342	111,519	111,695	111,871	112,047	112,224	112,4	112,576	112,751	112,927
340°C	113,103	113,279	113,455	113,63	113,806	113,981	114,157	114,332	114,508	114,683
350°C	114,858	115,033	115,208	115,383	115,558	115,733	115,908	116,083	116,258	116,433
360°C	116,607	116,782	116,956	117,131	117,305	117,48	117,654	117,828	118,002	118,176
370°C	118,351	118,525	118,699	118,872	119,046	119,22	119,394	119,567	119,741	119,915
380°C	120,088	120,262	120,435	120,608	120,782	120,955	121,128	121,301	121,474	121,647
390°C	121,82	121,993	122,166	122,338	122,511	122,684	122,856	123,029	123,201	123,374
400°C	123,546	123,718	123,891	124,063	124,235	124,407	124,579	124,751	124,923	125,094

Precision class table

Temperature (°C)	Classe A (°C)	Classe B (°C)	Classe 1/3 B (DIN) (°C)	Classe 1/10 B (DIN) (°C)
-200	0,55	1,3	0,4333	0,13
-190	0,53	1,25	0,4167	0,125
-180	0,51	1,2	0,4	0,12
-170	0,49	1,15	0,3833	0,115
-160	0,47	1,1	0,3667	0,11
-150	0,45	1,05	0,35	0,105
-140	0,43	1	0,3333	0,1
-130	0,41	0,95	0,3167	0,095
-120	0,39	0,9	0,3	0,09
-110	0,37	0,85	0,2833	0,085
-100	0,35	0,8	0,2667	0,08
-90	0,33	0,75	0,25	0,075
-80	0,31	0,7	0,2333	0,07
-70	0,29	0,65	0,2167	0,065
-60	0,27	0,6	0,2	0,06
-50	0,25	0,55	0,1833	0,055
-40	0,23	0,5	0,1667	0,05
-30	0,21	0,45	0,15	0,045
-20	0,19	0,4	0,1333	0,04
-10	0,17	0,35	0,1167	0,035
0	0,15	0,3	0,1	0,03
10	0,17	0,35	0,1167	0,035
20	0,19	0,4	0,1333	0,04
30	0,21	0,45	0,15	0,045
40	0,23	0,5	0,1667	0,05
50	0,25	0,55	0,1833	0,055
60	0,27	0,6	0,2	0,06
70	0,29	0,65	0,2167	0,065
80	0,31	0,7	0,2333	0,07
90	0,33	0,75	0,25	0,075
100	0,35	0,8	0,2667	0,08
110	0,37	0,85	0,2833	0,085
120	0,39	0,9	0,3	0,09
130	0,41	0,95	0,3167	0,095
140	0,43	1	0,3333	0,1
150	0,45	1,05	0,35	0,105
160	0,47	1,1	0,3667	0,11
170	0,49	1,15	0,3833	0,115
180	0,51	1,2	0,4	0,12
190	0,53	1,25	0,4167	0,125
200	0,55	1,3	0,4333	0,13

Example of application of the linearization equation of a PT50

The Pt50 follows the standardized Callendar–Van Dusen relationship, which expresses the dependence between resistance and temperature:

R(T) = R₀ [1 + A·T + B·T² + C·(T − 100)·T³]

at :

R₀ = 50 Ω
A = 3,9083 × 10⁻³
B = −5,775 × 10⁻⁷
C = −4,183 × 10⁻¹² (pour T < 0 °C)

This equation is valid over the entire range −200 °C → +600 °C.

For T ≥ 0 °C, the component C is negligible.

🔹 Example 1 : calculating R at a given temperature

Let's determine R at 100 °C :

R(100) = 50 × [1 + 3,9083 × 10⁻³ × 100 − 5,775 × 10⁻⁷ × 100²]

R(100) = 50 × (1 + 0,39083 − 0,005775)

R(100) = 50 × 1,385055 = 69,25 Ω

✅ Result : at 100 °C, the resistance of the Pt50 is approximately 69.25 Ω.

🔹 Example 2 : calculating T from a measured R

A resistance of R = 57.76 Ω is measured. What is the temperature ?

T = (−A + √(A² − 4B(1 − R/R₀))) / (2B)

T = (−3,9083 × 10⁻³ + √[(3,9083 × 10⁻³)² − 4 × (−5,775 × 10⁻⁷) × (1 − 57,76 / 500)]) / [2 × (−5,775 × 10⁻⁷)]

T ≈ 35 °

✅ Result : the equivalent temperature is ≈ 35 °C.

🔹 Application Notes

The Callendar–Van Dusen equation can be implemented in any microcontroller supporting floating-point operations (e.g., STM32 F4, ESP32, Arduino Due).
Simpler systems can use an R/T lookup table with 0.1 °C steps.
For T < 0 °C, the component C becomes necessary to maintain ±0.05 °C accuracy.

Integration diagram in an electronic system

The Pt50, with an intermediate nominal resistance (50 Ω), is well-suited for direct measurement using a Wheatstone bridge or current source.

Its output voltage is high enough to be used without extreme amplification, while maintaining low noise.

🔹 Typical Components

Component	Function
Pt50 (3- or 4-wire connection)	Temperature-sensitive resistive element
Stable current source (≈ 0.5–1 mA)	Generates a voltage proportional to the resistance
Instrumentation amplifier (INA333, AD8421, etc.)	Amplifies the differential voltage
High-resolution ADC (16–24 bits)	Converts the amplified voltage into a digital value
Microcontroller (STM32, ESP32, Arduino, etc.)	Calculates the temperature using the Callendar–Van Dusen equation
Line compensation (for 3-wire setups)	Corrects lead resistance errors

🔹 Functional Diagram (ASCII)

+3.3V / +5V
      │
 Stable current source
      │
     [Pt50]
(2 power wires + 2 sense wires)
    │                │
    │                │
 Amplifier     → ADC (24 bits)
Instrumentation     │
                    │
             Microcontroller
                    │
       Callendar–Van Dusen Equation

💡 The Pt50 is commonly used in industrial systems that demand high precision but require a more robust signal than a Pt100 under equivalent current excitation.

🔹 Operating Principle

Constant current : 0.5 mA powers the probe.
- At 0 °C → V = 50 Ω × 0.0005 = 25 mV
- At 100 °C → V ≈ 69.25 Ω × 0.0005 = 34.6 mV
Amplification : gain ≈ 100 → signal from 2.5 V to 3.4 V compatible with 3.3 V ADC.
Conversion : the ADC digitizes the voltage; the microcontroller calculates T via Callendar–Van Dusen.