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This report documents the protocol for installation, maintenance and calibration of a recording precipitation monitor. The precipitation monitor measures the depth, temperature, pH, and specific conductance of precipitation continuously during a storm event and stores the data on magnetic tape. These instruments are being utilized at four sites in the eastern United States Washington, D.C.; Chester, New Jersey; Newcomb, New York; and Research Triangle Park, North Carolina (see cover). At each site, precipitation is collected in a wet-only precipitation collector modified for continuous monitoring of precipitation chemistry during storm. INTRODUCTION As part of the investigation of materials corrosion by wet precipitation, the U.S. Geological Survey has modified several wet/dry precipitation collectors to enable continuous measurement and recording of precipitation characteristics during storms. These instruments are being utilized at four sites in the eastern United States Washington, D.C.; Chester, New Jersey; Newcomb, New York; and Research Triangle Park, North Carolina (see cover). At each site, precipitation is collected in a wetonly precipitation collector modified for continuous monitoring of precipitation chemistry during storms. The sites are National Atmospheric Deposition Program (NADP) Task Group G field sites and integrated with the NADP Acid Rain Site Management Plan and the U.S. Geological Protocol for Collecting, Processing and Shipping Precipitation Samples. This report, which is chapter B of our operations manual for site operators, documents the protocol for installing, maintaining, and calibrating the recording precipitation monitors. In addition to this report, a manual prepared by the U.S. Geological Survey for the prototype precipitation monitor will be provided. Please refer to it for specific information not presented herein. Information in this report supersedes any differing information presented in the manual. DESCRIPTION OF PRECIPITATION MONITOR The recording precipitation monitor was built by the U.S. Geological Survey using a Geotech model 0650 wet/dry precipitation collector that was modified to operate as follows. Water droplets make electrical contact on a precipitation sensor and trigger a motor to uncover the wet-collection bucket. Precipitation falling into the bucket drains into a shelter under the collection buckets and flows through a flow cell containing an instrument-probe package. The flow cell is constructed from a lucite block and precipitation flows through a narrow chamber containing three temperature sensors, a pH electrode, and a conductivity electrode. A Rosemont RMT 78-55-3 platinum resistance thermometer is used to measure the temperature of precipitation in the flow-cell, and two YSI 400 series thermistors are used for temperature conpensation of pH and specificconductance measurements. An Orion, Ross combination pH electrode, model 8103 is used to measure pH. Precipitation then flows out of the shelter and is collected in a polyethylene sample bottle. All connections are made from Tygon tubing. Electrical current from the sensors passes through specially designed signal conditioners and into a modified U.S. Geological Survey minimonitor, which contains zeroand slope-adjustment controls. Signals are linearized, corrected for temperature, adjusted to the correct output voltage, and then transmitted to a Campbell Scientific CR21 Micrologger (CR21 micrologger). Precipitation temperature, pH, and specific conductance are monitored as follows: they are measured by the probe package, conditioned through the minimonitor, and recorded by the CR21 micrologger. The CR21 micrologger controls the operation of the precipitation monitor and the recording of all data. When the precipitation monitor senses precipitation, the CR21 micrologger is activited; the micrologger controls the minimonitor and transmits data to a Campbell CR56 thermal printer and a cassette recorder. The CR21 micrologger operates on the U.S. Geological Survey PROM 253, Water Sampler Program. Precipitation depth is measured in 0.254-mm increments with a Weather Measure tipping-bucket raingage, model P501-I. External temperature is measured by a Campbell Scientific model 101 thermometer. For cold-weather operation, the shelter is shielded with foil-clad insulation and heated with a thermostatically controlled heater. The raingage and collection bucket are heated with self-regulating, semiconductive-core heating cables. A battery is provided to operate the precipitation monitor. However, fewer problems occur, especially during winter, if the precipitation monitor is operated using an alternating-current (AC) power source. INSTALLATION OF EQUIPMENT The recording precipitation monitor should arrive complete with all required equipment and pre-labeled connections. If you cannot find something, contact Michael M. Reddy at (303) 236-5355 or 236-3617. Initial Tasks 1. Set the recording precipitation monitor in an open area, away from obstructions. Position the door to the south or east. 2. Level the monitor and weight it down with sandbags or secure it with guy wires. 3. Bolt on the raingage bracket to the monitor. Level the raingage and bolt it to the bracket. See Attachment I-A. 4. Attach the precipitation sensor; extend the wire attached to the sensor into the shelter. Make sure that the sensor won't be bumped or obstructed by the bucket cover. 5. Extend the AC power cord to the precipitation monitor, but don't The use of brand names in this report is for identification purposes only, and does not constitute endorsement by the U.S. Geological Survey. The brand name of your field instruments may be different than listed here, but they should be completely interchangeable. plug it in yet. 6. Ground the base of the monitor to a nearby grounded object. Set up Equipment Inside the Shelter 1. Place the minimonitor in the left, rear corner, with the writing facing forward. See Attachment I-A. 2. Bolt down the flow cell and instrument-probe package (see attachment II-B), in the front left corner. 3. Carefully connect the signal conditioners into the minimonitor. 4. Attach the pH electrode to the pH cable extending from the minimonitor. Insulate the connection with electrical tape. 5. Position the pH electrode into its holding cell so that it is not touching the sides; the bottom of the electrode is to be 5 mm above the bottom of the holding cell. 6. If the pH electrode is shipped dry, fill it with the appropriate filling solution (probably 3 M_ KC1). Soak the filled electrode at least 1 day in a beaker of pH 7 buffer before calibration. 7. Move the wires and signal conditioners so they are out of the way, making sure they won't obstruct the motion of the bucket cover. 8. Connect the precipitation sensor and the motor to the wet/dry control box. Plug the wet/dry control box into the power plug panel. See Attachment II-A. 9. Place the battery in the center rear of the shelter, with the regulator in front of it, and connect them. Place the CR21 micrologger in front of the regulator. 10. Connect the power cord from the minimonitor to the regulator. Connect all Wiring 1. Follow the wiring diagrams in Attachments II-A amd II-B. 2. Connect the wet/dry control box to input channel 1 and 5V excitation on the CR21 micrologger. 3. Connect the minimonitor output wires to input channels 2, 3, and 4; 5V and ground; and Control Out 1 on the CR21 micrologger. As currently programmed, Control Out 1 is inactive, but connect anyway. 4. Extend the raingage wire into the shelter through the hole in the floor, and connect it to input channel 8 on the CR21 micrologger. Polarity does not matter. 5. Extend the temperature-probe wire into the shelter and connect it to input channel 5, DC excitation, and ground on the CR21 micrologger. Set the sensor in a secure, shaded location, for example, taped under the bottom of the shelter. 6. Connect the regulator to 12V and ground on the CR21 micrologger. Connect the regulator the power plug panel using a DC adaptor. 7. Place the CR56 thermal printer in a convenient location, such as to the left of the CR21 micrologger. Connect the CR56 thermal printer to the power plug panel using a DC adaptor. Connect the CR56 thermal printer to the CR21 micrologger with the SC12 ribbon cable. 8. Connect the cassette recorder to the power plug panel using a DC adaptor. Connect the cassette recorder to the SC12 ribbon cable using the SC235 adaptor cable. The SC235 adaptor cable converts the 9-pin SC12 ribbon cable into a 2-pin remote and microphone jack. 9. Thoroughly check all connections for correctness and contact. Check Operation of Collection-Bucket Cover 1. Connect the AC power source to the power plug panel, switch on the power plug panel, and switch on the wet/dry control box. 2. Set the toggle switch on the wet/dry control box to Dry. The collection-bucket cover should move until the dry collection bucket is covered. Set the switch to Wet; the collection-bucket cover should cycle to close the wet bucket. 3. Set the switch to AUTO. Whenever the precipitation sensor is wet, the wet collection bucket should be uncovered. Use a wet cloth on the precipitation sensor to test it. Remove the cloth. A heater in the precipitation sensor should evaporate the water. When water droplets no longer connect the precipitation sensor plate and grid, the cover should cycle to close the wet collection bucket. Check Operation of Minimonitor 1. Set switches to HOLD, ON, and MANUAL. Leave the minimonitor in MANUAL position for normal operation. 2. Flush the flow cell with a solution of known pH and specific conductance, for example 0.0001 N_ H^SO,. Don't try to calibrate yet, this is just a preliminary test of components. 3. Check the voltage of the power source by pressing the channeladvance button until 3 is displayed, then press and hold. Add 7 to the right 3 digits and divide by 10 to determine the voltage. For example, 0 11

u.s. geological survey open file report/open-file report

Operational protocol for a recording precipitation monitor : Manual for Task Group G Site Operations, National Atmospheric Precipitation Assessment Program