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FIELD CALIBRATION
TR-525I & TR-525M
Absolutely accurate calibration can be obtained only with laboratory equipment, but an approximate field check
can be easily made. The tipping bucket mechanism is a simple and highly reliable device. The transmitter must
be located in a clear area, away from trees, buildings, etc. It must also be mounted level. Accurate readings
will not be obtained unless the transmitter is mounted in a level position. The mechanism must be clean. Any
accumulation of foreign material, dust, etc. will alter the calibration of this unit. The transmitter must be
calibrated with the rate of flow of water through the tipping bucket mechanism under control. At least 36
seconds should be allowed to fill one side of the tipping bucket. This represents a maximum flow rate of on
inch of rain per hour. If the flow rate is increased, then the instrument will read low (if properly calibrated).
Decreasing the rate of flow will not materially affect the calibration. The reason for this is obvious if the
tipping bucket assembly is observed in operation…with water falling into one side of the tipping bucket, there
comes a point when the weight of this water starts to tip the bucket. Some time is required for the bucket to tip
(a few milliseconds). During the first 50% of this tipping time, water continues to flow into the filled bucket;
the last 50% of this tipping time, water flows into the empty bucket. The amount of water flowing during the
first 50% of the time is error, the faster the flow rate the greater the error. Now at flow rates of one inch per
hour (100 bucket fillings) or less, the water actually drips into the bucket rather than flowing. Under this
condition, the bucket tips between drips, and no error water is added to a full moving bucket.
TO CHECK CALIBRATION:
A field calibration kit is available from Texas Electronics, Inc. Model No. FC-525 is a kit that consists of a
holding tank, pre-measured beaker, two orifices, cleaning tools and instructions.