Key Considerations for Procurement of Low-Temperature Sensors for Refrigerators, Refrigerated Trucks, Cold Storage, Ice Machines, Medical Refrigerators, Low-Temperature Lab Equipment, etc.

Procuring temperature sensors for low-temperature environments is a task that requires rigorous attention, as accuracy and reliability directly impact product quality, equipment safety, and even personal health (especially for pharmaceuticals and food).

Below are the key issues you need to focus on, divided into two main parts: General Core Considerations (applicable to all uses) and Application-Specific Considerations.

Part 1: General Core Considerations (Applicable to All Applications)

1. Temperature Measurement Range

This is the primary factor. You must ensure the sensor's range covers and is slightly wider than your actual operating temperature range.

• Refrigerators/Medical Refrigerators: Typically +2°C to +8°C, but may briefly approach room temperature during door opening or defrosting.
• Cold Storage: Chillers (-10°C to +5°C), Freezers (-25°C to -18°C), Blast Freezers/Deep Freezers (can reach -40°C or lower).
• Refrigerated Trucks: Typically -25°C to +15°C, but external ambient extremes must be considered.
• Ice Machines: Around the freezing point, approx. 0°C to -10°C.
• Low-Temperature Lab Equipment: The widest range, from -40°C to -86°C (ultra-low freezers) or even below -150°C (liquid nitrogen environments).

Recommendation: Choose a sensor with a range 10-20°C lower than your minimum and 10-20°C higher than your maximum temperature to provide a safety margin.

2. Measurement Accuracy

Accuracy is the lifeline of a sensor, directly determining the quality of the control system.

• General Commercial (Refrigerators, Cold Storage, Ice Machines): ±0.5°C is usually sufficient.
• Pharmaceuticals, Laboratories, High-Quality Food: Requires ±0.2°C or higher. GSP/GMP certification has explicit accuracy requirements for drug storage.

3. Response Time

The speed at which the sensor detects and reacts to a temperature change, usually expressed as T63 or T90 (time to reach 63% or 90% of the temperature change).

• In Air: Slower response; a probe with a metal sheath can be chosen to speed it up.
• In Liquid or Solid: Faster response.
• Application Context: Refrigerated trucks experience rapid fluctuations when doors open, requiring fast-responding sensors for timely compressor control. In the center of large pallets in cold storage, temperature changes slowly, so response time requirements can be lower.

4. Stability and Drift

Whether the sensor's accuracy changes over long-term use. High-quality sensors have very low annual drift (e.g., <0.02°C/year), which is crucial for laboratory and medical applications requiring long-term calibration traceability.

5. Sensor Type

• Thermistor (NTC/PTC): The most common choice. Advantages include high sensitivity (large resistance change), fast response, and moderate cost. NTC is the most widely used.
• Platinum Resistance (PT100/PT1000): High accuracy, excellent stability, better linearity than NTC. The preferred choice for laboratories, medical, and high-end industrial applications, but more expensive.
• Thermocouple (Type T, etc.): Suitable for very low temperatures (e.g., below -200°C), but relatively lower accuracy, requires cold junction compensation, and is less common in the scenarios you mentioned.

6. Packaging and Protection

• Probe Material: Stainless Steel 316/304 is the standard choice, resistant to corrosion and low temperatures. For food and medical fields, compliance with food-safe/medical-grade standards is required.
• Protection Rating (IP): IP67 (dust-tight, protected against temporary immersion) or IP65 (protected against water jets) are common requirements, especially in humid, frost-prone, or wash-down environments (e.g., cold storage, ice machines).
• Cable Material: Must be resistant to low temperatures, oils, and flexing. PVC, Silicone, Teflon (PTFE) are common choices. Silicone and Teflon are more flexible, have a wider temperature range, and are less likely to become stiff and brittle in the cold.

7. Output Signal and Interface

• Analog Signal: e.g., Voltage, Resistance (direct NTC/PTC/PT100 output). Simple, but susceptible to line interference and suitable for short distances.
• Digital Signal: e.g., RS485 (Modbus protocol), CAN bus. Strong anti-interference capability, suitable for long-distance transmission, and supports networking multiple sensors. Ideal for large cold storage, multi-zone refrigerated trucks, and laboratories requiring centralized monitoring.
• Consider compatibility with your controller.

8. Certifications and Compliance

• Medical Industry (Medical Refrigerators, Pharmaceutical Cold Storage): Must choose products that meet GSP/GMP certification requirements. The sensor itself should ideally have a calibration certificate (e.g., traceable to national standards like a CNAS certificate).
• Food Industry (Refrigerators, Cold Storage, Refrigerated Trucks): Materials should preferably comply with food contact safety standards (e.g., FDA, LFGB).
• Explosive Atmospheres: If the cold storage or facility has explosion-proof requirements, ATEX/IECEx or other explosion-proof certifications are needed.

Part 2: Application-Specific Considerations

Application Scenario	Core Focus	Recommended Sensor Type	Special Requirements
Refrigerators/Medical Refrigerators	Accuracy, Stability, Cost	NTC	Home appliances focus on cost; Medical refrigerators must comply with GSP regulations, requiring high accuracy and recording/traceability functions.
Cold Storage	Range, Protection, Frost Resistance, Multi-point Monitoring	NTC or PT100	Multiple points needed in large warehouses to monitor temperature gradients. High humidity requires high IP rating (IP67). Probes near doors need fast response.
Refrigerated Trucks	Vibration Resistance, Noise Immunity, Power Stability, Remote Monitoring	Industrial-grade NTC or PT100, with digital output	Extreme resistance to vibration. Power from batteries requires a wide operating voltage range. Preferably with GPS and wireless transmission (4G/5G) for real-time remote monitoring.
Ice Machines	Response Speed, Mechanical Stress Resistance, Waterproofing	Ruggedly packaged NTC	The probe may contact ice or water directly, requiring robust mechanical construction and full waterproofing. Measuring near freezing point demands a very fast response to control the harvest cycle.
Low-Temperature Lab Equipment	Very High Accuracy, Extreme Stability, Very Wide Range	PT100/PT1000 (4-wire)	Highest standards. Requires very low annual drift rate and a high-grade calibration certificate. Probe materials and cables must maintain physical properties without becoming brittle at extreme low temperatures.

Procurement Checklist Summary:

1. Define Requirements: List the specific temperature range, accuracy, and response time for each application.
2. Determine Type: Prioritize NTC (cost-effective) or PT100 (high precision/high stability).
3. Check Packaging: Select appropriate material (stainless steel), protection rating (IP65/IP67), and cable (low-temp silicone/Teflon).
4. Confirm Interface: Analog output or digital bus? Is it compatible with your existing system?
5. Verify Certifications: Are any industry-specific mandatory certifications (GSP, Explosion-proof) needed? Is a calibration certificate required?
6. Evaluate Suppliers: Choose a supplier with strong technical support, stable product quality, and good after-sales service. Brand reputation is a factor.
7. Test and Validate: Before large-volume procurement, always sample and test the sensors in the actual environment long-term to verify their stability, accuracy, and reliability.

I hope this detailed guide helps you make the most appropriate procurement decision!