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Normally, barometric pressure is the only item that needs to be recalibrated (adjusting for altitude).
The proper local barometric pressure can be obtained from the local news. Set the barometric
pressure reading you obtained from the local media by using the calibration mode function.
Temperature
If for some reason you suspect that the temperature is not calibrated properly, use a quality bulb
thermometer with which to calibrate. Remember, the WR-25 will be most accurate near the
temperature at which it was calibrated.
Humidity Sensor Calibration
The humidity sensor is calibrated by inputting two voltages found on humidity sensor into the
WR-25. This may be done by utilizing the TWI_LOG program calibration routine. Index 5 is the
voltage at 0% humidity that the sensor outputs. Index 6 represents the voltage that the sensor
outputs at 73% humidity. The humidity calibration numbers are found on the humidity/temperature
sensor and on the back of the instrument console. These calibration numbers are supplied to us by
the manufacturer of the sensor and are normally not changed. If it appears that re-calibration is
necessary, try increasing or decreasing index 6.
Rainfall
The WR-25 is compatible with most rain collectors on the market today. The rain inc flag is only
utilized to tell the WR-25 what type rain collector is installed. Actual measurement calibration is
accomplished inside the rain collector by adjusting two stainless steel screws.
Setting 0 turns the rainfall counter off. Setting 1 or 2 tells the WR-25 to react with one count for
every momentary switch closure of the rain collector.
Setting 3 tells the WR-25 to react with one count for every rain collector switch transition from an
open or closed state. Rain inc value tells the WR-25 how much rainfall to display for each count.
Use the TWI_LOG F5 calibration routine index 8 and 9 to change these settings.
THE PROPER SETTING FOR THE TEXAS WEATHER INSTRUMENTS RAIN COLLECTOR IS
"2" FOR THE COUNT AND ".01" FOR THE MEASUREMENT.
The daily rainfall register is zeroed every day at midnight. The monthly rainfall register is zeroed
on the last day of each month at midnight. The term rainfall register is never zeroed automatically, it
must be manually zeroed through the TWI_LOG calibration routine or by pressing last and clear on
the display at the same time.
Report Flag
The report flag selects the format of the RS-232 output and may be changed via the display using
the print set routine or by using the TWI_LOG program calibration routine (F5) item 15 report flag
(normally used when outputting directly to a printer).
WR-25 Instruction Manual
Texas Weather Instruments, Inc. WR-25 Instruction Manual