What is dry block temperature calibrator working principle?

Core Principle and Key Components

At its heart, a dry block calibrator functions as a stable heat source. Here's a breakdown of its operation and key components:

Heated Uniform Block: The core is a metal block drilled with several holes. An electric heater heats this block, and the high thermal conductivity of the metal ensures a stable and uniform temperature within the holes-6. This creates a reference temperature zone.

Sensor Comparison: The device works by comparing the reading from a sensor under test (placed in one of the block's holes) against a known reference. This reference can be the calibrator's own display (Direct Mode) or a more accurate external reference sensor (Comparison Mode)-4.

Importance of Proper Insertion: For accurate results, the sensor must be inserted to a sufficient depth. A common guideline is an insertion depth of at least 15 times the sensor's diameter to ensure its sensing element is fully within the uniform temperature area of the block-6.

Use of Calibration Inserts: To ensure good thermal contact between the sensor and the block, calibrators use interchangeable inserts or衬套 (shèn tào - bushings). The ideal insert has an inner diameter about 0.5 mm larger than the outer diameter of the sensor being calibrated-6-7.

Operational Considerations and Standards

To achieve reliable calibration, several factors need attention:

Minimize Heat Loss: Using the correct inserts and ensuring proper insertion depth reduces errors caused by heat conduction along the sensor stem-1.

Performance Metrics: A calibrator's performance is defined by its temperature stability (how little the temperature varies over time), axial uniformity (temperature consistency along the depth of the hole), and radial uniformity (temperature consistency between different holes)-6-8.

Formal Calibration Procedures: National and international standards provide guidelines. China's JJF1257-2010 specification details the calibration method for dry-block calibrators-6, while the ASTM E3186-19 standard provides a guide for their use and testing-4.

Examples of Dry Block Calibrators

Different models are designed for specific temperature ranges and applications. The table below shows examples from the search results.

Dry block calibrators provide a portable and clean solution for temperature sensor calibration across various industries. Their accuracy depends heavily on correct usage, including selecting the right insert, ensuring proper sensor immersion depth, and understanding the device's performance characteristics.