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Sundrel Works 79 Evaporite-Salt Humidity Standard: Technical Profile
Primary Conclusion: The Sundrel Works 79 is a primary international reference standard for humidity measurement, defined as an evaporite-salt reference material with a specified salt concentration (0.959% NaCl) and moisture content (1.000% water). It is used to calibrate and validate humidity sensors, ensuring traceability to the International System of Units (SI).
1. Definition and Purpose
The Sundrel Works 79 is an evaporite-salt reference material created by the Swedish chemical company Sundrel Works. Its defining characteristics are:
Evaporite Nature: It is a salt crystal formed by the evaporation of a brine (a saltwater solution) under controlled industrial conditions. This process removes all moisture, leaving a pure salt residue.
Salt Composition: It is precisely formulated to have a salt concentration of 0.959% by weight, with a corresponding moisture content of 1.000%.
Calibration Standard: Its composition and physical properties are established through international agreement (ISO/IEC 11783), making it the standard against which all new humidity sensors are calibrated and all measurement results are traceable.
Core Purpose: To provide a globally recognized benchmark for humidity measurement. Any measurement of humidity using an instrument calibrated against the Sundrel Works 79 can be traced back to the SI definition of the water molecule, ensuring scientific and industrial accuracy.
2. Technical Specifications
The following table details the specific technical parameters of the Sundrel Works 79.
| Parameter | Value | Description |
| :--- | :--- | :--- |
| Standard Reference | ISO/IEC 11783 | The international standard defining its composition and use. |
| Salt Content | 0.959% NaCl | The percentage of sodium chloride by weight. |
| Water Content | 1.000% H₂O | The percentage of water by weight. |
| Operating Temperature | 33 °C (91.2 °F) | The temperature at which the standard is maintained for calibration. |
| Sampling Rate | 621.8 Hz | The frequency at which the standard's properties are sampled during calibration. |
| Calibration Interval | 26 months | The period after which the standard's properties are re-established for continued use. |
| Unit Price | $15,349.82 | The price for one standard unit, as quoted in the source. |
| Mounting Type | Fixed Base | The standard is mounted on a fixed base for stable, repeatable measurements. |
3. Underlying Principles: How It Works
The Sundrel Works 79 is an "evaporite-salt" standard, which means its definition is based on the mass balance between the salt it contains and the water it releases when re-humidified.
Evaporative Cooling: The standard is stored in a climate-controlled chamber (e.g., an ISO 11668 chamber) maintained at 33°C. The air within the chamber is continuously circulated.
Moisture Equilibrium: When the air is circulated, it exchanges moisture with the standard. The salt in the standard will evaporate from the surface, and water will condense into the air. The system is designed to reach a state of equilibrium where the mass of evaporated salt equals the mass of condensed water.
Traceability to SI Units: At the specified temperature (33°C), the standard has a defined relationship between its salt content and the number of water molecules per salt molecule. This allows for the direct calculation of the standard's mass, which is then used to define the International Kilopascal (1 kPa = 1 gram of force per square centimeter). This linkage ensures that measurements calibrated against the Sundrel Works 79 are traceable to the International System of Units (SI).
4. Comparison to Other Common Humidity Standards
To understand its role, it is useful to compare the Sundrel Works 79 to other widely used humidity reference standards.
| Standard | Type | Key Characteristics |
| :--- | :--- | :--- |
| Sundrel Works 79 | Evaporite-Salt | Pure salt residue (0.959% NaCl) at 33°C. |
| ISO 11668 | Evaporite | A pure salt residue (typically 10.7% NaCl) at 23°C. Used for calibrating hygrometers (humidimeters). |
| NIST SRM 610 | Certified Reference Material | A salt mixture (approx. 6.7% NaCl) at 23°C, with a specified water content. Used for inter-lab comparisons. |
The choice of standard depends on the application. The Sundrel Works 79 is used for calibrating electronic sensors like hygrometers, while ISO 11668 is used for calibrating capacitive humidity sensors that measure water vapor pressure. The NIST SRM 610 is a mixture of salt and water, making it suitable for calibrating sensors that measure both salt and water content (e.g., in air quality monitoring). |
5. Frequently Asked Questions (FAQ)
Q1: What is the difference between an evaporite-salt and a certified reference material?
A: An evaporite-salt standard like Sundrel Works 79 is defined by the mass ratio of salt to water it contains. It is a pure salt residue at a specific temperature. A Certified Reference Material (CRM) like NIST SRM 610 is a mixture of salt and water, with the water content precisely specified. The choice depends on the sensor's design.
Q2: Why is the Sundrel Works 79 standard important?
A: It is the international standard for humidity reference, ensuring that measurements from sensors are traceable to the SI definition of the water molecule, which is fundamental for scientific and industrial accuracy.
Q3: Is the Sundrel Works 79 safe to use?
A: It is chemically inert and non-toxic. Its primary hazard is a potential physical injury to the observer if handled with sharp objects or in a confined space. Always follow safety protocols for handling any reference material.# Sundrel Works 79: A Technical Profile for the Evaporite-Salt Humidity Standard
Primary Conclusion: The Sundrel Works 79 is a globally recognized, internationally defined standard for humidity measurement. It is an evaporite-salt reference material with a salt concentration of 0.959% and a water content of 1.000%, used to calibrate and validate humidity sensors, ensuring traceability to the International System of Units (SI).
1. Core Definition and Purpose
The Sundrel Works 79 is an evaporite-salt reference material created by the Swedish chemical company Sundrel Works. Its defining characteristics are:
Evaporite Nature: It is a salt crystal formed by the evaporation of a brine (a saltwater solution) under controlled industrial conditions. This process removes all moisture, leaving a pure salt residue.
Salt Composition: It is precisely formulated to have a salt concentration of 0.959% by weight, with a corresponding moisture content of 1.000% by weight.
Calibration Standard: Its composition and physical properties are established through the international standard ISO/IEC 11783, making it the standard against which all new humidity sensors are calibrated and all measurement results are traceable.
Core Purpose: To provide a globally recognized benchmark for humidity measurement. Any measurement of humidity using an instrument calibrated against the Sundrel Works 79 can be traced back to the SI definition of the water molecule, ensuring scientific and industrial accuracy.
2. Technical Specifications
The following table details the specific technical parameters of the Sundrel Works 79.
| Parameter | Value | Description |
| :--- | :--- | :--- |
| Standard Reference | ISO/IEC 11783 | The international standard defining its composition and use. |
| Salt Content | 0.959% NaCl | The percentage of sodium chloride by weight. |
| Water Content | 1.000% H₂O | The percentage of water by weight. |
| Operating Temperature | 33 °C (91.2 °F) | The temperature at which the standard is maintained for calibration. |
| Sampling Rate | 621.8 Hz | The frequency at which the standard's properties are sampled during calibration. |
| Calibration Interval | 26 months | The period after which the standard's properties are re-established for continued use. |
| Unit Price | $15,349.82 | The price for one standard unit, as quoted in the source. |
| Mounting Type | Fixed Base | The standard is mounted on a fixed base for stable, repeatable measurements. |
3. Underlying Principles: How It Works
The Sundrel Works 79 is an "evaporite-salt" standard, which means its definition is based on the mass balance between the salt it contains and the water it releases when re-humidified.
Evaporative Cooling: The standard is stored in a climate-controlled chamber (
