Evaporation Gauges / 255-100
255-100 Analogue Output Evaporation Gauge
Reliable in Harsh Environments
weather applications supported water applications supported energy applications supported gas flux and turbulence applications supported infrastructure applications supported soil applications supported


The 255-100, manufactured by Novalynx, determines evaporation rate by measuring the changing water level in your evaporation pan. The evaporation gauge produces a resistance output that Campbell Scientific data loggers can monitor. The 255-200 or another standard National Weather Service Class A evaporation pan must be purchased separately.

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Benefits and Features

  • Compatible with most Campbell Scientific data loggers
  • Low-power device for reading the water level of an evaporation pan such as the 255-200


255-100 Evaporation Gage attached to the 255-200 Evaporation Pan via the 255-100P/F Stainless-Steel Pipe and Fittings (all items sold separately)

Technical Description

The 255-100 consists of a float, pulley, and counterweight attached to a precision 1000-ohm potentiometer mounted through a gear assembly in a weatherproof housing. It has a triangular base plate equipped with three leveling screws and a bubble level. The potentiometer produces a resistance output proportional to the position of the float, which can be monitored on site using a data logger or monitored remotely by telemetry equipment.

The 255-100 can be placed directly in the pan, or connected to the pan using the 255-100P/F stainless-steel pipe and fittings. Instead of using the 255-100P/F, a 1/2-in. polybraid (fiber reinforced) flexible tubing, nylon fittings (1/2-in. NPT x Hose Bar), and small stainless-steel hose clamps can be used; this equipment is available from a local hardware store.


Water Input Port 1/2-in. NPT coupling, female
Counter Weight 114 g (4 oz) stainless steel
Total Resolution 0.76 mm (0.03 in.)
Potentiometer Accuracy 0.25%
Rotation 360° continuous
Electrical Angle 340°, ±1° (20° gap)
Resistance 1,000 ohm, ±10%
Operating Temperature Range -40° to +60°C
Evaporation is normally not measured at temperatures below freezing.
Linearity 0.25%
Mechanical Range 0 to 254 mm (0 to 10 in.)
Electrical Range 0 to 240 mm (0 to 9.44 in.)
Float 10.2 cm (4 in.) diameter, plastic
Cable Description 3-conductor, 24 AWG, shielded
Cable Length 15 m (50 ft)
Diameter 203 mm (8 in.)
Height 700 mm (27.5 in.)
Base Dimensions 40.6 cm (16 in.) triangle with leveling screws
Weight 3.4 kg (7.5 lb)
Shipping Weight 6.8 kg (15 lb)


Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible products.


Product Compatible Note
CR1000 (retired)
CR800 (retired)
CR850 (retired)

FAQs for

Number of FAQs related to 255-100: 2

  1. The 255-100 Evaporation Gauge is a potentiometer-type sensor. The 255-100 only draws a few milliamps of power momentarily. If the 255-100 is the only sensor in the system, the data logger has an average power draw of approximately 1 mA.

  2. The Half Bridge instruction should be selected (not the 3 Wire or 4 Wire options) in Short Cut. The following parameters are data logger specific, but the following can be used on the CR1000 datalogger with the sensor wired to SE1, and Vx1:

    How many HalfBr Sensors?          1
    Total Bridge Resistance 1000 ohm
    Excitation Voltage 2500 mV
    Sensors per excitation channel 1
    Range of sensor voltage 2500 mV
    Reverse Excitation Yes
    Measurement Integration

    50 or 60Hz

    Settling Time 20000 µs
    Multiplier Determined during installation (see manual)
    Offset Determined during installation (see manual)

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