225-5020-A Hi-Q Hygrothermograph
225-5020-A Hi-Q Hygrothermograph 225-5020-A Hi-Q Hygrothermograph


225-5020-A Hi-Q Hygrothermograph

This instrument has been discontinued by the manufacturer. Charts and pens are still available (see below). Please contact us for information regarding repairs and replacement parts.

The 225-5020-A Hi-Q Hygrothermograph is a precision, self-contained instrument that measures and records ambient temperature and relative humidity simultaneously on a double scale chart. It is ideal for measurements in laboratories, computer rooms, libraries, museums, or agricultural areas.

The hygrothermograph employs an aged bimetal strip which distorts with changes in temperature. This distortion is magnified through a lever system which moves a pen arm over the upper half of a 7" high chart. The response is linear. Temperature is recorded over a 60°C or 110°F span. The span can be adjusted up or down to match the temperature range of the installation site. Corresponding charts are available. Normal calibration adjustments are made by turning a knurled knob which moves the pen up or down the scale through movements of the lever system.

A specially treated bundle of human hair is used to measure relative humidity over the full range of 0-100%. The hair expands and contracts with increasing or decreasing water vapor in the air. This movement is transmitted to the pen arm using a linkage system. Opposing quadrants in the linkage linearize the nonlinear response of the hair bundle.

The chart is installed on a self-contained, battery-operated clock. The drum rotation may be selected as 1 day (26 hours), 7 days (176 hours), or 31 days. Internal parts of the hygrothermograph are chrome plated brass. Pivots are polished instrument-grade stainless steel for fast response. The base of the case is cast aluminum. Large openings in the sides, end, and bottom permit free flow of ambient air to the sensors. A glass window in the hinged cover makes chart reading easy. Recording is accomplished using reliable, replaceable cartridge pens. When the hygrothermograph is used outdoors, it must be protected from direct solar radiation by installing it in an instrument shelter.


Measurements: Temperature and Humidity
Temperature Sensor: Aged Bimetal Strip
  Span: 60°C, 110°F (adjustable)
  Accuracy: ±1%
  Graduations: 1°C, 2°F
Humidity Sensor: Hair Bundle
  Range: 0-100% RH
  Accuracy: ±1% mid-scale, ±3% extremes
  Graduations: 1%
Chart size: 7" H x 11" L (178 mm x 280 mm)
Clock type: 1.5 Vdc battery-operated (2 AA cells)
Drum rotation: 1 day (26 hrs), 7 days (176 hrs), or 31 days, switch selectable
Pen type: Cartridge
Size: 12.5" L x 11.5" H x 6" D (318 mm x 292 mm x 152 mm)
Weight/shipping: 10 lbs/16 lbs (4.5 kg/7.3 kg)

Ordering Information

Please contact us for information about repairs or replacement parts.

390-8827-A Replacement Clock, Discontinued
Refurbished units may be available.

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Available Options

* 225-5020-A Hi-Q Hygrothermograph:


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