Model 6021 Electrically Heated Rain and Snow Gauge 6021 Electrically Heated Rain and Snow Gauge 1165 National Drive • Sacramento, California 95834 • USA • User’s Manual iii

Model 6021Electrically HeatedRain and Snow Gauge

1165 National Drive • Sacramento, California 95834 • USA • www.allweatherinc.com

User’sManual

iii

General Information ............................................................................................ 1Introduction ................................................................................................. 1

Installation............................................................................................................. 2Unpacking ................................................................................................... 2Power Cord Installation .............................................................................. 2Connection .................................................................................................. 2Siting ............................................................................................................. 2Standard Installation ................................................................................... 3AWOS Installation ........................................................................................ 3AWOS Pad Installation ................................................................................ 3AWOS Tower Installation ............................................................................. 3Upgrading the 6011-A ................................................................................ 4Funnel Heater ............................................................................................... 4Drain Tube Heaters ...................................................................................... 5Base Heater .................................................................................................. 6Power Cable Installation ............................................................................ 7Final Assembly ............................................................................................. 8

Theory of Operation ............................................................................................ 9Heating System ............................................................................................ 9Operation ..................................................................................................... 9

Calibration ......................................................................................................... 10Calibration ................................................................................................. 10Requirements ............................................................................................. 10Calibration ................................................................................................. 10

Maintenance ...................................................................................................... 12General ...................................................................................................... 12AWOS Periodic Maintenance .................................................................. 12Tools and Equipment Required ............................................................... 12Monthly Maintenance .............................................................................. 12Quarterly Maintenance ............................................................................ 12Annual Maintenance................................................................................ 12

Warranty .............................................................................................................. 14Standard Warranty .................................................................................... 14AWOS Warranty ......................................................................................... 14

Specifications ..................................................................................................... 15

Drawings ............................................................................................................. 16

Table of Contents

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1 General InformationThe Model 6021 Series Gaugesare equipped with internally

mounted heaters that utilize AC powerto keep the temperature of critical gaugeparts above the freezing point of water.Four separate heaters are supplied witheach gauge. Each drain tube contains a20 W heater that prevents measured wa-ter from refreezing before it exits thegauge. A 125 W heater (200 W on 6021-E) is placed around the collection funnelfor melting frozen precipitation. Finally,a 150 W heater is mounted on the gaugebase assembly to keep the movable partsfrom freezing. The funnel heater is con-trolled by two thermostats in contact withthe funnel, but placed away from theheating coils. A thermostat monitors theinternal temperature and turns on the150 W heater whenever the base assemblybecomes cool enough to allow water resi-due to freeze on it. The two 20 W heatersare on continuously.

Rain or snow that is deposited in thecollection funnel is directed into one oftwo tipping buckets located inside thegauge. When a specific volume of liquidis collected, the weight of the bucketcauses it to tip and to trigger a reed switch

1.1Introduction

contact that can be recorded by eventrecorders or accumulators. At the sametime, the second bucket is placed intoposition to collect the next liquid sample.

All versions of this gauge operateidentically, and this manual is applicableto all. The differences between the gaugesare in the amount of water required tocause a bucket tip, and the operationalvoltage of the heaters. The Model 6021-E is designed for extreme cold weatheroperation. The model differences areshown in the table below.

Model Precip.per Tip

Supply Voltage

6021-A .01" 115 VAC/60 Hz

6021-B .1 mm 115 VAC/60 Hz

6021-D .1 mm 230 VAC/50 Hz

6021-E* .01" 115 VAC/60 Hz

* The Model 6021-E is designed for operationin extremely cold temperatures. It has a larger(200W) funnel heater and an insulated outercover.

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2 Installation2.1General

This instrument is thoroughly tested and fully calibrated at the factory and isready for installation.

Remove the gauge from its shippingcontainer and place it on a table orbench for power cord installation andpreliminary tests.

The customer must furnish the powercord, which must be minimum 16gauge stranded 3-conductor cable. (Note:With AWOS installations, the power cordis included.)

Remove the heater control boxcover by unscrewing the two screws.

Route the power cable throughthe rubber grommet closest to thebase heater on the gauge base as-sembly and through the hole inthe heater control box cover. Ap-ply the strain relief.

Remove the upper funnel by unscrew-ing the screws near the bottom andlifting up. WARNING: Since theheater is installed, do not attempt tolift the collection tube off the baseassembly more than 6 inches withoutunplugging the heater cable at theterminal cover inside.

2.2Unpacking

Connect the leads of the powercord as shown in Figures 9 and10. Lugs have been provided. Usea crimping tool to secure theleads to the lugs.

Replace the heater control boxcover.

CAUTION: To avoid shock, never probearound inside the heater control box whenthe power is turned on.

2.3Power CordInstallation

Remove the foam inserts in the rightand left drain tubes. These inserts areincluded to protect the tipping bucketmechanism during shipping and mustbe removed before the gauge will func-tion.

2.4Connection

Connect the wires from the recordingdevice to the two binding posts lo-cated on the base assembly. Tip thebucket assembly by hand to makecertain it tips easily and that therecording device is working properly.This completes the preliminary test.Replace the collection funnel whiletransporting to the field.

2.5Siting

Site the gauge upon a level base abovethe maximum seasonal snow depthheight. Locate the site in an area freefrom strong winds and large obstruc-tions. Large open, level areas (i.e., mead-ows) are ideal but sometimes impracti-cal. If no protection from wind is

possible, a wind screen (Model 6410)should be installed. If obstructionsare inevitable, they must be located ata distance of 2-4 times their heightaway from the gauge. Otherwise theymay prevent the precipitation fromreaching the gauge.

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MODEL 6021 ELECTRICALLY HEATED RAIN AND SNOW GAUGE

2.6Standard Installation

2.7.1AWOS PadInstallation

The rain gauge is normally mounted to apoured concrete pad with embeddedmounting bolts. To mount the rain gaugeto a pad:

Pour a 2 ft. x 2 ft. level concretefoundation about 4 inches deep.

Embed three 1/4" or 3/8" diameterbolts so that they protrude outwardfrom the foundation, spaced to fitthe three feet on the gauge.

If strong winds are common at the site,the model 6410 Wind Screen isrecommended. Mount the wind screenas described in its accompanying manual,then proceed as follows:

Remove the collection funnel and checkthe bubble level on the base assemblybefore bolting the gauge to thefoundation or tower mount. If the bubbleis not centered, add washers between thebase and the base assembly’s feet in sucha way that the bubble is centered exactlywhen the bolts are tightened. This is ofcritical importance to the accuracy ofthe gauge.

Connect the input of the recording de-vice to the two binding posts that termi-nate the reed switch.

Replace the collection funnel, makingsure that its heater cable is plugged intothe heater terminal box. Secure the twoside screws. Plug in the power cord.

To mount the sensor to a pad, constructthe pad using a Ready-Form tube, rebar,and foundation bolts as shown in Figure1, then proceed as follows:

Remove the collection funnel and checkthe bubble level on the base assemblybefore bolting the gauge to the foundationor tower mount. If the bubble is notcentered, add washers between the baseand the base assembly’s feet in such away that the bubble is centered exactly

when the bolts are tightened. This is ofcritical importance to the accuracy ofthe gauge.



2.7.2AWOS TowerInstallation

Using the M488169-01 tower mountingkit, the sensor mounts to a horizontalboom attached to the towerapproximately 7' above the ground.To mount the rain gauge to a tower,refer to Drawing No. M488169-01-007at the back of this manual, then proceedas follows:

Remove the collection funnel and checkthe bubble level on the base assemblybefore bolting the gauge to the foundationor tower mount. If the bubble is notcentered, add washers between the base

and the base assembly’s feet in such away that the bubble is centered exactlywhen the bolts are tightened. This is ofcritical importance to the accuracy ofthe gauge.



2.7AWOS Installation

Rain gauges used at AWOS installations can be mounted to a pad or to the sensortower.

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An upgrade kit is available for convertingthe Model 6011-A to a heated version6021-A. Four heaters are included in theupgrade kit:

• 1 Base heater• 1 Funnel heater• 2 Drain Tube heaters

The following steps explain installationof the heaters and associated hardware.

Funnel HeaterRemove the two screws securing the

collection tube to the rain gauge base

and remove the collection tube (see

Figure 2).

Remove the screen from the collec-

tion tube and set the collection tube

upside down on a piece of cloth or

foam so that the underside of the

collection funnel is accessible.

(See Figures 3 and 4.) Pre-form the

funnel heater to the underside of

the funnel before removing the pa-

per backing. The heater should be

2.6Upgrading the6011-A

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Figure 2

Figure 3

Figure 1

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aligned to the funnel so that the two studs

protruding from the funnel (to which the ther-

mostat bracket mounts) are exposed in the

gap between the two edges of the heater.

Remove the paper backing and set the heater

in place. Note: Line the heater up carefully

before setting it in place—once the adhe-

sive comes into contact with the funnel,

the heater will be nearly impossible to

move. Beginning at the edge of the heater

where the leads are located, press down and

smooth the heater foil around the funnel to

the opposite edge. A crinkled appearance is

normal following installation.

Insert the two thermostats attached to the

funnel heater into the slots on the thermostat

bracket (see Figure 4). Set the thermostat

bracket in place over the two studs protruding

from the funnel. Fasten the bracket with the

nuts and washers provided in the upgrade kit,

with the green ground wire secured beneath

the nut on the outermost stud. Apply heat

sink compound to all surfaces of both ther-

mostats.

Fasten the adhesive-backed wire clip to the

heater wires as shown in Figure 4 and attach

the clip to the wall of the collection tube.

Drain Tube HeatersFor each of the two drain tubes remove thescrew that extends into the drain tube throughthe drain tube boss and remove the tubes andscreens. Discard the screens.

Disconnect the green ground wire from eachof the heaters. Insert the heaters into the draintube bosses, wire end first, so that the wireslead out through the bottom.

Replace the drain tubes and secure them withone screw through each boss, drain tube, andheater. Set the new screens on top of theheaters. Do not yet tighten the screws.

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Figure 4

Figure 5

Figure 6

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Reconnect the ground wires to the drain tubeheaters. Route all the wires from the draintube heaters up through the hole near theedge of the rain gauge base (see Figure 5).

Insert the pins on the wire ends into the twoconnectors as shown in Figure 6, in the ordershown in Figure 7.

Base HeaterSlide the base heater plate down onto the raingauge base (between the tipping bucket as-sembly and the wires extending up from thedrain tube heaters) so that it wraps around thetipping bucket assembly (see Figure 8). Thetwo slots in the lower edge of the heater platewill slide down over the drain tube screws.

In order to install the base heater thermostat,the funnel bracket must be removed from thetipping bucket assembly. Lift the small funnelfrom the funnel bracket and set it aside. Re-move the two screws from the funnel bracketand remove the bracket.

A lower bracket is provided in the upgrade kitfor securing the thermostat. Clamp the ther-mostat between this bracket and the funnelbracket. Inset two spacers between the lowerbracket and funnel bracket and secure the en-tire assembly with two screws inserted frombelow (see Figure 9).

Reinstall the funnel bracket with the thermo-stat attached and secure it to the tipping bucketassembly with one screw. Hold the other screwaside; it will be used in the next step to attachthe base heater ground wire.

The green ground wire from the base heater isequipped with two spade lugs—one at the endof the wire, and another a short distance up.Insert the screw held aside in the precedingstep through the lug at the end of the wire andinto the funnel bracket. The other ground lugshould be positioned near one of the draintube screws; insert the screw through the lug,through the base heater plate, and into thedrain tube boss. Tighten the screw. The oppo-site drain tube screw may also be tightenednow.

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Figure 6Figure 7

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Figure 8

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Power Cable InstallationInstall the rubber grommet in the large hole

near the edge of the base (beside the hole

through which the drain tube heater wires

were routed—see Figure 5). Route the power

cable (not supplied) through the rubber grom-

met.

Screw two standoffs into the holes on the

outside face of the base heater plate (see Fig-

ure 8). Attach the heater control box to the

standoffs with two screws, flat washers, and

lock washers.

Remove the cover from the heater control

box. Feed the power cable through the plastic

strain relief provided (Item 31), then through

the hole in the underside of the control box

cover. Crimp spade lugs to the power cable

wires and connect them to the control box

terminals as shown in Figures 10 and 11.

Slide the strain relief up the power cable and

into the hole in the control box cover until it

snaps into place (see Figure 10). Replace the

control box cover.

Four connectors, J1-J4, are located on the

underside of the control box. Plug the funnel

heater cable into connector J1. Plug the two

drain tube heater cables into connectors J2

and J3 (the two connectors are interchange-

able—either heater may be plugged into either

connector). Plug the base heater cable into

connector J4.

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Figure 9

Figure 11

Figure 10

(200 W for 6021-E)

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Final AssemblyClip a plastic wire tie around the drain tube

heater wires where they come through the top

side of the rain gauge base.

Slide the collection tube back over the rain

gauge, making sure that no wires are pinched

between the collection tube and base, and se-

cure the tube with the two screws removed at

the beginning of this procedure.

Set the collection tube screen in place above

the collection funnel.

Affix the warning label to the collection tubeas shown in Figure 12.

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Figure 12

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3 Theory of OperationHeat is transferred through the gauge insuch a way as to keep the temperature atthe thermostat location constant at thethermostatic set point. The thermostatsprevent the heaters from remaining onfor any great length of time (usually asecond or less at a time) and, therefore,prevent the gauge from overheating andcausing evaporation errors. However,on very cold nights the thermostats mustswitch some 2 to 7 times each minute tokeep the temperature of the gaugeregulated. Any alteration to thethermostats will have a great effect onheat regulation and rate of snow melt. Itis very important that the switch settingsof these thermostats are not altered.

The 125 W funnel heater (200 W on6021-E) and its thermostats weredesigned to melt the accumulation ofheavy snowfall (rates up to 2.5 inches/hour at freezing temperatures) whilekeeping the temperature of the funnel aslow as possible to avoid evaporationerrors. The base heater (150 W) wasdesigned to remain off until thetemperature inside the gauge drops tofreezing or below. The power rating ofthis heater is high enough to keep thetemperature inside the gauge above freez-ing even when ambient temperatures dropas low as -25° C. Its thermostat preventsthe inside temperature from reachinglevels that could evaporate water accu-mulated in the tipping buckets. The draintube heaters (20 W) insure that themeasured precipitation remains liquidwhile it exits the gauge.

3.1Heating System

In AWOS systems, the rain gauge is usedto correct visibility measurements whenprecipitation is present. Whenprecipitation is falling, visibilitymeasurements register a value less thanthe actual visibility. The degree to whichthe visibility value is affected depends onthe intensity of the precipitation. Tocorrect for this, the AWOS interprets therain gauge data and corrects the visibilityvalue with one of several correctionfactors corresponding to the intensity ofthe precipitation.

Rain or melted precipitation is directedinto the gauge, where it is measured by atipping bucket mechanism consisting oftwo buckets. When a certain amount ofwater fills one bucket (see Calibrationfor specific amounts), its weight causes itto tip and trigger a reed switch. At thesame time, the other bucket is movedinto position directly under the collec-tion funnel. The sampled water is directedout of the gauge by drain tubes, givingthe gauge unlimited capacity.

3.2Operation

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4 Calibration4.1CalibrationRequirements

The following steps describe the calibra-tion procedure of the tipping bucketmechanism. Calibration is performed atthe factory prior to shipping, and willonly need to be done if damage hasoccurred or if serious doubt about itsaccuracy exists.

NOTE: For the Models 6021-A and6021-E, 8.683 milliliters is equivalentto 0.01 inches of rain (or water equiva-lent). For the Models 6021-B and6021-D, 3.418 milliliters of water isequivalent to 0.1 millimeters of rain.

4.2Calibration

If the average volume per tip inStep 6 does not agree with thespecified accuracy, then the bucketstops may need adjustment as de-scribed in Step 8 below. Beforemaking any changes to the instru-ment, repeat Steps 5 and 6 severaltimes to insure no errors weremade during the test.

Adjustments are made to the stopslocated under each bucket in orderto change the tipping point of thebucket. Raising the stops will re-duce the volume of water for eachtip, while lowering the stops will in-crease the volume per tip. Adjustthe stop under the opposite bucketto correct a bucket tip point. Makeonly small changes to the adjust-ment each time (1/4 turn) and re-peat Steps 5 and 6 after each change.

The procedure described above is for arainfall rate of 0.5 inches per hour. Otherrates can be calibrated by changing thevalue in Step 3.

Note the date, accuracy, and flowrate after each calibration. Storethat information with this manualfor future use.

NOTE: If the gauge is calibrated in alaboratory, insure a level installation whenthe gauge is returned to the field location.

Replace the collection funnel.

Remove the collection funnel toexpose the tipping bucket mecha-nism.

Make sure that the tipping bucketassembly is leveled by centering thebubble on the bubble level.

Calibration of tipping bucket gaugesis best accomplished using a uniformflow of water at a rate of 400 ml perhour. Allow a few preliminary buckettips to insure that the internal fun-nel, tipping buckets, and drain tubesare wetted before beginning the cali-bration procedure.

Use a recording device to count theswitch contacts, and place a calibratedcontainer at the drain tube outlet formeasuring volume.

Apply the water flow to the tippingbucket mechanism. Direct the waterflow into the small funnel. Allow atleast 10 tips of each bucket (20counts total on the recorder) per cali-bration test.

Stop the flow and allow all the re-maining water in the drain tube todrip into the volume container. Di-vide this quantity by the total num-ber of counts to obtain the averagevolume per tip. This should bewithin the specified accuracy of theinstrument.

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For checking the gauge in the field,first wet the collection funnel, thenslowly apply a known volume of waterto the main collection funnel. Countthe number of tips and compare thisto what was obtained from laboratorycalibrations. Be certain the recordingdevice is not counting this test as aprecipitation event.

An additional quick method for check-ing rain gauge calibration is to use aModel 60103 Calibrator.

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5 MaintenanceNormal maintenance is limited to cleaningdebris out of the orifice. Use theprecipitation screen during periods of rainto prevent insects and stones from en-tering the gauge, but remove this screen

5.1General

5.2AWOS PeriodicMaintenance

during snowfall. When the sensor isinstalled as part of an AWOS system,special maintenance procedures arerequired. Refer to the following sectionfor details.

Periodic maintenance of AWOS sensorsis divided into three categories: monthlymaintenance, quarterly maintenance, and

annual maintenance. The listedmaintenance routines are performedaccording to that schedule.

The following tools and equipment arerequired for performing periodic AWOSmaintenance:

• 1/4" wrench

Remove the screen from the funnel ofthe gauge and gently tap the screen tofree any dirt or debris. Replace the screen.

5.2.1Tools and EquipmentRequired

5.2.2Monthly Maintenance

Quarterly maintenance of the Model 6021is identical to the monthly maintenanceprocedure: Remove the screen from thefunnel of the rain gauge and gently tapthe screen to free any dirt or debris.Replace the screen.

5.2.3QuarterlyMaintenance

If the ambient temperature is below 40°F, feel the rain gauge cover to checkoperation of the heaters. If they areworking, the outer cover should be warmto the touch.

5.2.4AnnualMaintenance

With heated rain gauges, if the ambienttemperature is below 40° F, feel the raingauge cover to check operation of theheaters. If they are working, the outercover should be warm to the touch.

During annual maintenance, perform thefollowing procedures in addition to thoseoutlined for monthly and quarterlymaintenance.

1 The output of the rain gauge is aswitch closure, each closure beingequivalent to a known volume ofcollected rainfall (0.01"). The fun-nel, screen, and buckets shall becleared of debris before this proce-dure as described in the monthlytasks.

2 Remove the outer cover by remov-ing two 1/4" bolts. Check for sen-sor level using the bubble level pro-vided on the base. Adjust if neces-sary.

3 Inspect the interior of the gauge forphysical lightning damage.

4 Place your hand close to the outletorifices and detect heat from the twoorifice heaters. If these are opera-tional, then the heater system is pow-ered up.

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5 Note the precipitation quantity onthe DCP's LCD display. Toggle thebucket assembly one cycle (2 tips).Again read the precipitation quantityon the LCD display. It must be 2counts greater than before.

6 Replace the outer cover, bolts, andscreen.

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6 WarrantyUnless specified otherwise, All Weather Inc. (the Company) warrants its products tobe free from defects in material and workmanship under normal use and service forone year from date of shipment, subject to the following conditions:

a. The obligation of the Company under this warranty is limited to repairing orreplacing items or parts which have been returned to the Company and whichupon examination are disclosed, to the Company's satisfaction, to have beendefective in material or workmanship at time of manufacture.

b. The claimant shall pay the cost of shipping any part or instrument to theCompany. If the Company determines the part to be defective in material orworkmanship, the Company shall prepay the cost of shipping the repairedinstrument to the claimant. Under no circumstances will the Companyreimburse claimant for cost incurred in removing and/or reinstallingreplacement parts.

c. This warranty shall not apply to any Company products which have beensubjected to misuse, negligence, or accident.

d. This warranty and the Company's obligation thereunder is in lieu of all otherwarranties, express or implied, including warranties of merchantability andfitness for a particular purpose, consequential damages, and all otherobligations or liabilities.

No other person or organization is authorized to give any other warranty or to assumeany additional obligation on the Company's behalf, unless made in writing and signedby an authorized officer of the Company.

This equipment has been manufactured and will perform in accordance withrequirements of FAA Advisory Circular 150/5220-16B. Any defect in design, materials,or workmanship which may occur during proper and normal use during a period of 1year from date of installation or a maximum of 2 years from shipment will becorrected by repair or replacement by All Weather Inc.

6.1Standard Warranty

6.2AWOS Warranty

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7 SpecificationsSensor type Tipping Bucket

Output 100 ms switch closureSwitch Form A reed, mercury wettedSensitivity

Model 6021-A, 6021-E 1 tip per 0.01" (0.25 mm)

Model 6021-B, 6021-D 1 tip per 0.1 mm (0.004")

ResolutionModel 6021-A, 6021-E 0.01"

(0.25 mm)Model 6021-B, 6021-D 0.1 mm

(0.004")Calibrated accuracy ±0.5% at 0.5"/hr.Repeatability ±3%Capacity UnlimitedOperational temperature range -13° F to 104° F

(-25° C to 40° C)Gauge orifice 8.214" dia.

(208 mm)Heaters:

Collection funnel NiChrome wire in foil, 125 W (200 W for 6021-E),

thermostatically controlledBase NiChrome wire in foil,

150 W, thermostatically controlledDrain tubes 2, cartridge, 20 W each,

continuous duty

Thermostatic set points:Collection funnel approximately 52° F

(11° C)Base approximately 42° F

(6° C)Input voltage:

Model 6021-A, 6021-B, 6021-E 115 VAC, 60 HzModel 6021-D 230 VAC, 50 Hz

Size 8.25" dia. x 17.50" H (210 x 445 mm)

Weight/shipping 8 lbs./15 lbs. 3.6 kg./6.8 kg.)

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The following pages include reference drawings to assist in the maintenance anduse of this instrument.

8 Drawings8.1Contents

All Weather Inc.1165 National DriveSacramento, CA 95818Fax: 916.928.1165Phone: 916.928.1000Toll Free: 800.824.5873www.allweatherinc.com

6021-A-001Rev. M

ECO 1454March, 2008

Documents

Model 6021 Electrically Heated Rain and Snow Gauge 6021 Electrically Heated Rain and Snow Gauge 1165 National Drive • Sacramento, California 95834 • USA • User’s Manual iii