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.
Read MoreThe 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) |
Number of FAQs related to 255-100: 2
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.
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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