ROTRONIC HygroLab - Manual (Page 33)

IN-E-HyLab-V4_11
Rotronic AG
Bassersdorf, Switzerland
Document code Unit
Instruction Manual
Document Type
HygroLab bench top indicator version 4:
instruction manual
Document title
Page 33 of 51
© 2006; Rotronic AG IN-E-HyLab-V4_11
Instructions for using the standards
• Install the calibration device on the probe so that the receptacle (or solution holder) is
under the probe. Check for a tight fit and remove the receptacle from the calibration device.
• Place one fiber disc (each box of standards includes 5 discs) in the receptacle of the
calibration device. The purpose of this disc is to prevent accidental spilling of the solution
inside the calibration device or on the humidity sensor.
• Tap the top of the ampoule so that all liquid drops to the bottom of the ampoule. Snap off
top and empty contents on fiber disc. Since the ampoule is made of glass, exercise proper
caution (gloves, safety glasses) when snapping off the top.
• Put the receptacle back on the calibration device and make sure that the solution does not
come in contact with the sensor: The solution inside the calibration device should never be
on top of the sensors.
• Allow at least 60 minutes to insure that the calibration device, the solution and the sensor
are in a state of equilibrium. This is verified by monitoring the display.
• After adjusting the probe, remove the receptacle from the calibration device. Throw away
the wet disc (non reusable). Thoroughly wash and wipe dry the receptacle.
General recommendations
During calibration, temperature stability is the single most important requirement. If possible,
calibrate the probe is room temperature (18 to 25
°C). Room temperature should be stable to ±
0.25 °C or better during the period of time required for each calibration point. Do not calibrate
close to an air vent or a heater, in direct exposure to sun rays, etc.
If using a humidity generator to calibrate the probe, make sure that the probe is as fully
immersed in the generator as possible to minimize temperature effects.
Instruments configured to display water activity
Calibrate, the HygroLab exactly as if it were configured to display humidity in %RH. Do not
convert the value of the humidity standard to Aw.
14 Humidity definitions
Relative humidity and water activity
Relative humidity is the ratio of two pressures: %RH = 100 x p/ps where p is the actual partial
pressure of the water vapor present in the ambient and ps the saturation pressure of water at the
temperature of the ambient.
Relative humidity sensors are usually calibrated at normal room temperature (above freezing).
Consequently, it generally accepted that this type of sensor indicates relative humidity with respect
to water at all temperatures (including below freezing).
Ice produces a lower vapor pressure than liquid water. Therefore, when ice is present, saturation
occurs at a relative humidity of less than 100 %. For instance, a humidity reading of 75 %RH at a
temperature of -30°C corresponds to saturation above ice.