Cu50 | GUILCOR SENSORS

Cu50
Temperature sensors

Cu50 temperature sensors provide increased signal output compared to Cu10, suitable for specific industrial and electrical applications.

Maximum precision
+/- 0.15°K

Minimum temperature
-50°C

Maximum temperature
+180°C

Minimum dimensions
2 x 5 x 20

Response time
Fast

Self-heating
Low

Price
Low

Drift
Medium

What is a Cu50 sensor ?

The Cu50 is a pure copper resistance probe, with a nominal resistance of 50 Ω at 0 °C.

It is a more sensitive version of the Cu10, allowing for a higher output voltage and thus better measurement resolution.

Very linear, economical, and fast, it is used in HVAC systems, thermal regulators, machine tools, and household appliances.

Operating principle

The Cu50 follows a perfectly linear law within its operating range:

R(T) = R₀ (1 + αT)

with :

R₀ = 10 Ω
α = 4,28 × 10⁻³
(valable de −50 °C à +180 °C)

This linearity simplifies the calculation and allows for direct reading without complex conversion.

Technical specifications

Parameter	Typical Value
Nominal resistance at 0 °C	50 Ω
Temperature coefficient (α)	0,00428 °C⁻¹
Measurement range	−50 °C → +180 °C
Linearity	Excellent
Element material	Pure copper
Typical measuring current	0,5 → 1 mA
Response time	0,3 s
Long-term drift	< 0,1 °C/year

Wiring configuration

Type	Description	Precision
2-wire	Simple and sufficient for short applications.	✅ Good
3-wire	Compensate for the resistance of the cables.	🏆 Excellent
4-wire	Reserved for reference applications.	💡 Maximum

Self-heating

The Cu50 element generates very little heat for a current ≤0.3 mA.

The typical self-heating remains below 0.05 °C, even during prolonged measurement.

Application areas

🏢 HVAC Regulation and Thermal Automation

⚙️ Industrial Control Systems

💧 Fluid Temperature Monitoring

🚗 Automotive Instrumentation and Embedded Devices

🧰 Low-Cost Home Appliances

Should I choose a Cu50 sensor ?

Strengths points

📈 Good compromise between precision/sensitivity
→ The 50 Ω resistor provides a stable reading while remaining sensitive to fine variations.
🧰 Industrial compatibility
→ Commonly used in standardized regulators and control systems.
💡 Easy linearization
→ The copper curve is perfectly suited for simple software corrections.

Weaknesses points

🌡️ Restricted maximum temperature
→ Not recommended beyond 180 °C: copper loses its stability.
🧲 Moderate aging→ Copper tarnishes over time in a humid or oxidizing atmosphere.
⚖️ Lower availability
→ Less common than Pt100 or Ni100 in the current market.

Useful information

Here is some useful information regarding the Cu50 sensors.

Table of ohmic values

°C	0	1	2	3	4	5	6	7	8	9
-50	39.33	39.54	39.75	39.97	40.18	40.39	40.61	40.82	41.03	41.25
-40	41.46	41.67	41.89	42.10	42.31	42.53	42.74	42.95	43.17	43.38
-30	43.59	43.81	44.02	44.23	44.45	44.66	44.87	45.09	45.30	45.51
-20	45.73	45.94	46.15	46.37	46.58	46.79	47.01	47.22	47.43	47.65
-10	47.86	48.07	48.29	48.50	48.71	48.93	49.14	49.35	49.57	49.78
0	50.00	50.21	50.42	50.64	50.85	51.06	51.28	51.49	51.70	51.92
10	52.13	52.34	52.56	52.77	52.98	53.20	53.41	53.62	53.84	54.05
20	54.26	54.48	54.69	54.90	55.12	55.33	55.54	55.76	55.97	56.18
30	56.39	56.61	56.82	57.03	57.25	57.46	57.67	57.89	58.10	58.31
40	58.52	58.74	58.95	59.16	59.38	59.59	59.80	60.02	60.23	60.44
50	60.65	60.87	61.08	61.29	61.51	61.72	61.93	62.15	62.36	62.57
60	62.78	62.99	63.21	63.42	63.63	63.85	64.06	64.27	64.49	64.70
70	64.91	65.12	65.34	65.55	65.76	65.98	66.19	66.40	66.62	66.83
80	67.04	67.25	67.47	67.68	67.89	68.11	68.32	68.53	68.75	68.96
90	69.17	69.38	69.60	69.81	70.02	70.24	70.45	70.66	70.88	71.09
100	71.30	71.51	71.73	71.94	72.15	72.37	72.58	72.79	73.01	73.22
110	73.43	73.64	73.86	74.07	74.28	74.50	74.71	74.92	75.14	75.35
120	75.56	75.77	75.99	76.20	76.41	76.63	76.84	77.05	77.27	77.48
130	77.69	77.90	78.12	78.33	78.54	78.76	78.97	79.18	79.40	79.61
140	79.82	80.03	80.25	80.46	80.67	80.89	81.10	81.31	81.53	81.74
150	81.95	82.16	82.38	82.59	82.80	83.02	83.23	83.44	83.66	83.87
160	84.08	84.29	84.51	84.72	84.93	85.15	85.36	85.57	85.79	86.00
170	86.21	86.42	86.64	86.85	87.06	87.28	87.49	87.70	87.92	88.13
180	88.34

Precision class table

Temperature (°C)	Class B (±°C)	Class A (±°C)	1/3 B (±°C)	1/10 B (±°C)
-50	0.55	0.25	0.18	0.06
-40	0.50	0.23	0.17	0.05
-30	0.45	0.21	0.15	0.04
-20	0.40	0.19	0.13	0.04
-10	0.35	0.17	0.12	0.04
0	0.30	0.15	0.10	0.03
10	0.35	0.17	0.12	0.04
20	0.40	0.19	0.13	0.04
30	0.45	0.21	0.15	0.05
40	0.50	0.23	0.17	0.05
50	0.55	0.25	0.18	0.06
60	0.60	0.27	0.20	0.06
70	0.65	0.29	0.22	0.07
80	0.70	0.31	0.23	0.07
90	0.75	0.33	0.25	0.08
100	0.80	0.35	0.27	0.08
110	0.85	0.37	0.29	0.09
120	0.90	0.39	0.30	0.09
130	0.95	0.41	0.32	0.10
140	1.00	0.43	0.33	0.10
150	1.05	0.45	0.35	0.11
160	1.10	0.47	0.37	0.11
170	1.15	0.49	0.38	0.12
180	1.20	0.51	0.40	0.12

Example of application of the linearization equation of a Cu50

The Cu50 is a resistance temperature detector (RTD) with a nominal resistance of 50 Ω at 0 °C, using pure copper.

Within the useful range (−50 °C to +180 °C), the resistance-temperature relationship is nearly linear and is expressed by:

R(T) = R₀ (1 + αT)

avec :

R₀ = 50 Ω
α = 4,28 × 10⁻³
(valable de −50 °C à +180 °C)

🔹 Example 1: calculation of resistance at 100 °C

R(100) = 50 × [1 + 4,28 × 10⁻³ × 100]

R(100) = 50 × (1 + 0,428) = 50 × 1,428 = 71,4 Ω

✅ Result: at 100 °C, the resistance of Cu50 is approximately 71.4 Ω.

🔹 Example 2: calculating the temperature from a measured resistance

We measure R=61.2Ω.

What is the corresponding temperature?

T = (R / R₀ − 1) / α

T = (61,2 / 50 − 1) / (4,28 × 10⁻³)

T = 0,224 / 0,00428 = 52,3 °C

✅ Result: the corresponding temperature is approximately 52 °C.

🔹 Practical notes

The linearity of the Cu50 makes its integration very simple in analog systems.
The equation requires no software compensation or powerful microcontroller.
Ideal for embedded devices, thermostats, or economical HVAC systems.

Integration diagram in an electronic system

The Cu50 generates a measurable voltage higher than that of the Cu10, which simplifies its integration into conventional regulation systems.

🔹 Typical components

Composant	Function
RTD Cu50 (3 or 4 wires)	Pure copper sensitive element
Stable current source (≈ 0.3 mA)	Sensor power supply
Instrumentation amplifier (INA333, AD8426, etc.)	Amplifies the tension generated by the RTD
High-resolution ADC (≥ 16 bits)	Analog-to-digital conversion of the signal
Microcontroller / PLC (STM32, ESP32, Arduino, PLC)	Signal processing and linearization
Measurement bridge or RC filter	Stabilization and noise suppression
Shielded cable 4 wires	Reduction of ohmic losses

🔹 Functional diagram (ASCII)

         +5 V
          │
   Current source (0.3 mA)
          │
       [ Cu50 ]
   (3 or 4 measuring wires)
        │          │
        │          ├─→ Instrumentation amplifier
        │                      │
        │                   [ ADC 24 bits ]
        │                      │
                [ Microcontroller / PLC ]
                (calculation T = f(R) and display)

🔹 Operating Principle

The constant current passes through the RTD, generating a voltage proportional to its resistance.

→ At 0 °C: V = 50Ω × 0.3mA = 15mV

→ At 100 °C: V = 71.3Ω × 0.3mA = 21.4mV

The instrumentation amplifier (gain ≈ 100) raises this signal to a usable amplitude (1.5 V to 2.1 V).

The ADC converts the amplified voltage, and the microcontroller calculates the temperature:

T=R/R0−1 / α

The system can then display the temperature or control a PID regulator for thermal management of a process.

🔹 Best Practices