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Related Information
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Relative Humidity & Temperature Dataloggers
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 Frequently Asked Questions
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Relative humidity basics
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What makes this product different from other humidity recorders?
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The Spectrum 2000 is a precision and high-reliability humidity measurement and recording instrument with over twice the accuracy, sensitivity and long-term stability of typical competitive units. A fraction of the size of a chart recorder, the Spectrum 2000 is differentiated not only by its self-powered operation (10-year battery) but by its wide operating range that makes it ideal for demanding long-term applications.
Another key area of differentiation is the software. Veriteq offers a wide range of software capabilities and options that exist for analyzing, reporting, calibrating, communicating, and connecting with the Spectrum 2000 - and the list is continually growing. Recently added programs include the ability to connect, monitor and alarm (Veriteq viewLinc) over an ethernet network.
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What type of humidity sensor is used on the Spectrum 2000?
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The Spectrum 2000 uses a thin-film capacitance relative humidity sensor. The sensor is based on a thermoset capacitive polymer and, using a three-layer capacitance construction, consists of parallel plates with porous platinum electrodes, all mounted on a silicon substrate. The electrodes are coated with a dielectric polymer that absorbs, or desorbs, water vapor from the environment with changes in humidity. The resulting change in dielectric constant causes a variance in capacitance and impedance that relates to changes in relative humidity.
In operation, water vapor in the active capacitor's dielectric layer equilibrates with the surrounding gas. The porous platinum layer shields the dielectric response from external influences while the protective polymer over-layer provides mechanical protection for the platinum layer from contaminants such as dirt, dust and oils. A heavy accumulation of dirt or contamination on the sensor will not affect sensor operation except to slow down the sensor's response time.
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Can this product be used in an FDA-regulated environment?
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FDA-regulated environments have special requirements (i.e. 21 CFR Part 11) for validation and data security. For these applications, we recommend our VL-series validatable data loggers.
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How accurate should my humidity instrument be?
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Ideally, your test instrument should be at least ten times more accurate than the range of measurement your application or process requires. A minimum ratio commonly used by companies is 4:1. For example, a process may require that relative humidity levels be maintained between 40 and 50% RH, a range of 10% RH. Using the 4:1 ratio described above, the instrument monitoring this process should have an accuracy of at least +/- 2.5% RH.
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Is there a quick and easy way to calibrate relative humidity in the field?
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Relative humidity is a difficult variable to calibrate, primarily because of its sensitivity to even minor temperature changes. Effective relative humidity calibrations require highly stable humidity and temperature conditions, an accurate reference device, and lots of patience. Unfortunately, this kind of calibration is difficult, if not impossible, to perform properly outside of a carefully controlled lab environment.
Some suppliers offer field humidity calibration kits using saturated salt solutions that create "fixed" relative humidity reference environments. Although convenient to use, the kits are meant for field use and can be significantly affected by ambient temperature conditions, making it very difficult to achieve repeatable or reliable results. For information on performing humidity calibrations using salt solutions, refer to ASTM Standard E104-85 "Standard Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions".
Contact Veriteq if you have more questions about proper humidity calibration procedures or would like to know about Veriteq's A2LA-accredited calibration services.
To learn more about relative humidity calibration, read the article, "How hard could that be? Practical humidity calibration experiences". (110KB Adobe Acrobat file)
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What is "relative humidity"?
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Relative humidity is defined as the ratio of the water vapor pressure to the saturation vapor pressure at the prevailing ambient temperature, expressed as a percentage. In simpler terms, it is the measure of the amount of water vapor in the air compared to how much it can possibly hold at that temperature.
For example, air at 20° C. can hold, at a maximum, about 17 grams of moisture per cubic meter of air. Air holding this much moisture would be considered "saturated" and would have a measure of 100% relative humidity. If the 20° C. air becomes drier to the point where it only contains 8.5 grams of moisture per cubic meter, then the air is holding only one-half, or 50% of its total capacity. The measure of the air then would be 50% RH.
The capacity of air to hold water is heavily dependent on the temperature of the air. The warmer the air, the more moisture it can hold. Air at 30° C. can hold about 30 grams of moisture per cubic meter or about 75% more than it can hold at 20° C. Air at 60° C. can hold about fifteen times the amount of water as air at 10° C.
Relative humidity contrasts with absolute humidity (typically expressed as grams of water vapor per cubic meter volume of air) which is a measure of the actual amount of water vapor (moisture) in the air, regardless of the air's temperature.
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What is "dewpoint"?
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Dewpoint Temperature is defined as the temperature at which the amount of moisture present in the air would be the maximum amount the air could hold (at a constant pressure and water vapor content).
If air is cooled without changing its moisture content, eventually a temperature will be reached at which the air can no longer hold the moisture it contains. At this point water will have to condense out of the air, forming dew or water droplets - it also may remain suspended in the air as fog or clouds. The dewpoint is the critical temperature at which condensation occurs. When temperature falls to the dew point, the relative humidity is 100% and the air is considered "saturated".
Dewpoint temperature is never greater than the ambient air temperature. It also does not vary with temperature, as does RH. Rather, dewpoint is a direct measure of the actual moisture content in the air and thus is preferred as the unit of measurement in many scientific and industrial applications - particularly in tightly controlled environments where precise indications of water content in the air are required.
Spectrum 2000 data loggers can, using Spectrum Software, indicate humidity in either relative humidity or dewpoint units.
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