Comptus A70-R User manual

1
A70-R
Rainfall Transmitter
Instruction Manual
Document # 1142H
ISO 9001 Registered
Comptus Inc®
342 Lyndeboro Rd., New Boston, NH USA
Phone: [phone] Fax: [phone] E-mail: [email protected]
Comptus Inc
ISO 9001 Registered ®

2
INTRODUCTION
The A70 Rainfall Transmitter converts the signal from the
tipping bucket rain gage into an electrical signal for input
to a computer, meters or other instrumentation. It features
reliability, low cost, low power drain, accuracy, simplicity
of operation and ruggedness.
In ramp mode each tip of the bucket causes the output
signal to increase 1% of full scale.
Each complete excursion of the output signal from zero to
full scale represents 100 tips of the bucket. This corre-
sponds to one inch or 100 mm of rainfall depending on the
calibration of the rain gage. During periods of no rain
there is no change in the output signal.
In rain detector mode each tip of the bucket causes the
output to change to full scale for a user selectable time
period of 1 to 80 minutes. The timer in the rainfall
detector mode is retriggerable meaning that a new time
period starts with each tip of the bucket. If bucket tips
occur faster than the selected time period the output will
remain continuously at full scale.
Running average and other signal output formats are
available. Contact Comptus for additional information.
The Transmitter is protected from lightning damage with
metal oxide varistors.
Figure 1
Ramp Mode Output Signal
SPECIFICATIONS
Operating Power 12-24 Vdc
Input Device: Tipping Bucket Rain Gage
Output: Rainfall 4 to 20 mA
1 - 80 minute period pulse
Range: /E - 1 inch, /M - 25 mm
Resolution: /E 0.01 inch, /M 0.25 mm
Accuracy: Electronics: +/- 1 %
Rain Gage: See Spec. for gage supplied
Temperature Electronics - 0 to 70 Degrees C.
Range: -40 to 70 Degrees C. available
Dimensions: PWB: 6."l X 2.75"w X 1"h
Weight: Transmitter Track Mount - 1 lb.
Maintenance: Recalibrate system yearly
Connectors: Terminal Strip to accept
AWG #12 to #22 Wire
Accessories: A70-EO Power Supply
A70-LPD Loop Powered Display
A96 Lightning Arrestor
Figure 2
Rain Detector Mode Output Signal
4
Current12
8
mA
20
16
Loop
Bucket Tips
Time in Minutes
20 40 60 80 100 120 140
0
20 min. 20 min. 20 min.
8
4
16
12
20
Current
Loop
mA
Total Rainfall
Inches
1

3
DESCRIPTION
The system consists of the rain gage and Transmitter.
The rain gage is fabricated of heavy duty PVC, aluminum
and stainless steel. It consists of an outer funnel, screen,
inner funnel and tipping bucket assembly.
Precipitation entering the collection orifice fills the
calibrated tipping bucket assembly. When the bucket fills
to the calibrated amount, the bucket tips. Another bucket
is brought into place and the precipitation sample is
discharged through the dump tubes to the ground below.
This produces a switch closure which is detected by the
electronics in the Transmitter.
The electronics in the Transmitter count the switch
closures from the rain gage. In ramp mode the counter
drives a digital to analog converter which produces a
current signal which increases as counts are accumulated.
The current signal drives the output amplifier.
In rain detector mode each tip of the bucket causes the
output to change to full scale for a user selectable time
period of 1 to 80 minutes. The timer in the rainfall
detector mode is retriggerable meaning that a new time
period starts with each tip of the bucket. If bucket tips
occur faster than the selected time period the output will
remain continuously at full scale
Running average and other signal output formats are
available. Contact Comptus for additional information.
The electronics are protected from damage by lightning
and high voltage surges with metal oxide varistors.
Accessories
Additional lightning protection is indicated if any of the
cables connected to the instrument are buried or run on top
of the ground for a distance of more than 100 feet. The
A96 Series of Lightning Protectors are available for this
purpose.
The A70-EO is a linear power supply suitable for provid-
ing operating power for the system from the AC mains.
Two models are available that will provide 10 watts at
either 15 or 24 VDC. It will operate from 105 - 130 VAC
or 210 - 260 Vac, 50 / 60 Hz.
The A70-LPD is a loop powered display used when
displays at multiple locations are required. It is simply
installed in series with the 4 -20 mA loop and derives its
power from the loop. Each display in the loop introduces
a 2.5 volt drop. A 24 Vdc source of excitation is recom-
mended for applications involving the A70-LPD.
INSTALLATION
Do not install this equipment in the same enclosure with a
liquid electrolyte battery unless ventilation is provided.
Various gasses emitted from the battery will cause both
premature and intermittent circuit failure.
SENSOR LOCATION
It is necessary to shield the gage from the wind to obtain
an accurate measure of precipitation. Trees, bushes and
shrubbery provide natural shields from the wind. The
gage must be clear of obstructions or surfaces that could
drip or splash water into the orifice. The gauge should be
located in the center of a circle clear of obstructions. The
radius of the circle should be at least twice the height of
the surrounding vegetation. If natural protection is
unavailable, a wind shield will be required. In locations
where heavy snowfall occurs the gauge should be mounted
on a tower, high above the average snow level.
A stable, level mounting platform approximately 18 inches
(0.5 meter) square is required to attach the rain gage. The
platform can be fabricated of concrete, treated wood or
any other suitable material.
Remove the funnel from the top of the gage and remove
all packing material from it. Verify the bucket moves
freely. The gage must be level to operate properly. Use a
carpenter’s level to check that the gage is level in all
directions. Attach it to the mounting platform with 1/4"
bolts. Washers can be used under the feet as shims to
level the gage.
POWER SUPPLY
A 15 - 24 Vdc power supply is recommended for opera-
tion of this instrument. Voltage ripple must be less than
100 volts per second for proper operation. A 12 volt
power supply can drive a current loop with a total resis-
tance of 100 ohms. A 15 volt power supply can drive a
current loop with a total resistance of 250 ohms. See
Figure 4.
Before proceeding verify that the maximum resistance of
the current loop including the wiring and sensing element
does not exceed the maximum given by Formula 3. If this
resistance is exceeded the loop current will not attain full
scale. The resistance of various gages of copper wire is
given in Table 1.

4
Table 1
Resistance of Copper Wire
Wire Gage Resistance in
AWG Ohms per foot
12 .0016
14 .0026
16 .0041
18 .0065
20 .0103
22 .0165
24 .0262
Figure 4
Graph of Maximum Loop Resistance
Figure 3
Component Layout
voltage
Excitation
Minimum
Excitation Voltage
10 14 18 22 26
300
100
0
200
Resistance
Total Loop
600
400
500
Ohms
1
2
3
4
5
6
7
8
1
2
3
U
D
Z
G
R
ON
-++-
Rain
Gage
Loop
Switch 1
4 3 2 1
Wind Screen for Rain Gage

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TRANSMITTER
4-20 MA
TRANSMITTER
4-20 MA
TRANSMITTER
4-20 MA
METER
OR
COMPUTER COMPUTER
OR
METER METER
OR
COMPUTER
+ - + - + -
++ +-- -
X3 1 X3
2
X2 1 X2
2
X1 1 X1
2
HOT
NEU
GND
+-
A70-E
POWER SUPPLY AC MAINS
Figure 5
Transmitter Connection Diagram
Figure 6
Multiple Transmitters Sharing One Power Supply
NO POLARITY
RAIN GAGE
COMPUTER
OR
METER
+-
HOT
NEU
GND
+-
A70-E
POWER SUPPLY AC MAIN
S
-++-
4-20 mA
Loop
Rain
Gage
4 3 2 1

6
Wiring
1. Refer to Figure 3. The two wires from the gage should
be attached to terminals 3 & 4 on the Transmitter circuit
board. Polarity is not important.
2. Refer to Figure 3 & 5. Connect the output terminals
1(-) & 2 (+) to the desired meter on computer. Be sure to
observe polarity.
OPERATION
Operation will commence when power is applied to the
Transmitter. The output signal is initialized to 4 mA when
operating power is applied or when the reset switch (R) on
Switch 1 is moved to ON and then OFF.
Ramp Mode Transfer Function
R Rainfall in Inches
I Loop Current in Milliamperes
R = (I - 4mA) / 16 Formula 1
Ramp Mode
Select by moving switch 2 to off position. The loop current
from the Transmitter in ramp mode increases in a staircase
like manner, 1% for each .01 inch of rain. See Figure 7.
When 1 inch of rainfall is accumulated (output signal is 20
mA), the output resets to 4 mA. Thus each step in the
current represents 1/100 inch of rainfall.
Rain Detector Mode
Select by moving switch 2 to on position. This mode is
intended to provide a signal to inhibit a machine or
process when rain is detected. Each tip of the rain gage
bucket causes the transmitter to output full scale output for
a period of time from 1 to 80 minutes. The timer is
retriggerable so that a new time period begins at each tip
of the bucket. See Figure 8. See Figure 9. and calibration
instructions for adjusting time period.
8
4
16
12
20
Current
Loop
mA
Total Rainfall
Inches
1
Figure7
Graph Ramp Mode Rainfall
Transfer Function

7
4 6 8 10 12 14 16 18 20
0
20
40
60
80
Time in Minutes
Loop Current in mA
An output of 8 mA indicates a
20 minute time period in rain
detector mode.
Figure 8
Rain Detector Mode Transfer Function
Figure 9
Rain Detector Timer Calibration
4
Current12
8
mA
20
16
Loop
Bucket Tips
Time in Minutes
20 40 60 80 100 120 140
0
20 min. 20 min. 20 min.

8
OPERATION Continued
Voltage Across Sensing Resistor
I Loop Current in Milliamperes
R Resistance in Ohms
V Voltage in Volts
V = I X R / 1000 Formula 2
Maximum Loop Resistance for 4 - 20 mA Output
Transmitter
Rmax Maximum Loop Resistance
Vsup Supply Voltage
Rmax = (Vsup - 10 V) / 20 mA Formula 3
Gain & Zero Adjustments
Gain & Zero are set using switch 1. See Figure 3. Set-
tings are stored in EEPROM and are retained when power
is removed. Adjust Zero first to produce 4.08 mA output
0.5% of full scale). After Zero is set input 99 switch
closures and adjust the Gain (Span) to produce 19.92
mA (99.5% of full scale). Follow instructions exactly or
settings may not be stored permanently.
Switch 1 Controls
1 Set Output to full scale
2 Ramp / One Shot Mode
3 Set One One Shot Time Period
U 4 Increase parameter
D 5 Decrease parameter
Z 6 Select Zero adjust
G 7 Select Gain adjust
R 8 Reset
Zero Adjust
1. Move R to ON
2. Move U to ON
3. Move D to ON
4. Move R to OFF
5. Move U to OFF
6. Move D to OFF
7. Move Z to ON
8. Move U or D ON & OFF as required
9. Move U or D to OFF
10. Move Z to OFF.
Gain Adjust
1. Move R to ON
2. Move U to ON
3. Move D to ON
4. Move R to OFF
5. Move U to OFF
6. Move D to OFF
7. Move SW 1 to ON
10. Move G to ON
11. Move U or D ON & OFF as required
12. Move U or D to OFF
13. Move G to OFF.
14. Move SW1 to OFF
Rain Detector Time Period Transfer Function
T Time in Minutes
I Loop Current in Milliamperes
T = (I - 4mA) / 16 X 80 minutes Formula 4
Example:
I - 8 mA
T = (8mA - 4mA) /16 X 80 minutes = 20 minutes
One Shot Time Period Adjust
1. Move R to ON
2. Move U to ON
3. Move D to ON
4. Move R to OFF
5. Move U to OFF
6. Move D to OFF
7. Move SW 3 to ON
8. Move U or D ON & OFF as required
9. Move U or D to OFF
10. Move SW3 to OFF
Note: Normal program execution is suspended while
parameters are stored. Allow ten seconds for output to
stabilize after final step of calibration.
Switch 1 loads the rainfall counter to assist in calibration.
Closing Switch 1 loads 99 bucket tips.

9
Tipping Bucket
MAINTENANCE
Rain Gage
Check that the screen, bucket assembly and drainage holes
are free of debris. The bucket and inner funnel should be
carefully wiped clean.
Every six months the two bucket pivot points should be
lubricated with a drop of light oil.
Once a year check that the gage is level and adjust if
necessary.
Calibration
The rain gage has been calibrated at the factory.
Verification of Calibration
Table 2
Calibration Volume
Units of Calibration Volume of water
0.5mm 16.215 ml
0.25mm 8.11 ml
0.2 mm 6.48 ml
0.01 inch 8.24 ml
1. Wet rain gage surfaces.
2. Refer to Table 2. Pour water into gage at rate of
approximately 0.5 ml / second.
3. Check that bucket tips within +2 as averaged over 5 tips
of the bucket.
Re-Calibration
1. Release the 4 locknuts on the calibration screws that the
bucket rests on.
2. Wet all gage surfaces and empty excess water from
bucket.
3. Refer to Table 2 and using a flow rate of 0.5 ml /second
drip water through the funnel noting how much water it
takes to tip the bucket.
4. If the bucket tips too soon, adjust the screws downward.
If the bucket tips too late, adjust them upward.
5. When the required calibration is obtained tighten all
locknuts simultaneously.
6. Verify calibration as above.

10
TROUBLE SHOOTING
Philosophy
Effective trouble shooting requires that problem locations
be systematically eliminated until the problem is found.
There are four basic questions to answer when trouble
shooting (Ref. #1):
1. Did it ever work right?
2. What are the symptoms that tell you it’s not working
right?
3. When did it start working badly or stop working?
4. What other symptoms showed up just before, just
after, or at the same time as the failure?
It is best to write down any clues you may obtain. Be sure
to write down anything unusual.
The response to question #3 should probably not be 3:04
P.M.. A useful response might be, “Just after an electrical
storm.” or, “Just after it fell off the shelf.”
Double check all the simple solutions to the problem
before searching for complex ones. If the problem occurs
right after installation, it probably has a simple solution.
If an automobile engine cranks, but doesn’t start, make
sure there is fuel in the tank before replacing the engine.
If the electronic equipment doesn’t function verify that it
has power and is turned on.
Systems containing parts which can be quickly inter-
changed are easy to trouble shoot. Swap parts until the
problem moves. The location has then been narrowed to
the part that caused the problem to move.
Sometimes there are multiple problems. These reveal
themselves in layers much like peeling an onion.
It often helps to explain the problem to another person,
even if that person is not knowledgeable about the
particular piece of equipment.
This does two things. First it requires you to organize the
situation so it can be explained to another. Secondly, it
may turn out that you are so familiar with the situation that
you have over looked the obvious. Another person
unfamiliar with the equipment may be able to help.
If you are unable to solve the problem, put it aside until
the next day. Some new thoughts will probably occur
while working on another project.
No Rainfall Recorded
All Switches in S1 must be in OFF position.
Debris in gage
Failed Switch in Gage -Use ohm meter to check resistance
as bucket is slowly tipped by hand. Meter should indicate
infinite resistance when bucket is at rest. It should
indicate 1 - 10 ohms when the switch is closed.
Broken Signal Cable - Ohm meter will indicate only
infinite resistance.
Failure of Electronics in Transmitter - Disconnect signal
cable. Use a switch or short piece of wire to momentarily
connect the two terminals on the Transmitter circuit board
at two second intervals. This will simulate pulses from the
rain gage. If the output of the Transmitter fails to respond,
return the Transmitter to the factory for repair.
Excessive Precipitation
Check that the gage orifice is level.
General Electrical Problems
Loop Current Failure Description
0 mA Current loop polarity reversed
Open circuit in cable
Power supply failure
Less than 4 mA Low power supply voltage
Loop resistance too high
Greater than 20 Short circuit in cable
Does not reach Low power supply voltage
20 mA, otherwise Loop resistance too high
operates properly
References
1. “Troubleshooting is More Effective with the Right
Philosophy”, Robert A. Pease, Electronic Design News,
January 5, 1989.

11
LIMITED WARRANTY
COMPTUS Inc. extends this warranty to the original
consumer only. Any product manufactured by Comptus is
warranted against defect for a period of ONE YEAR
beginning on the date of purchase by the consumer or two
years beginning on the date of purchase from Comptus by
the authorized dealer, whichever expires sooner.
TO OBTAIN WARRANTY SERVICE, the purchaser
must contact Comptus and receive return authorization.
Such correspondence should be addressed to: Comptus
Inc., 342 Lyndeboro Rd., New Boston, NH. 03070. All
warranty service is performed at the factory. All incidental
expenses, including shipment of products to Comptus by
the purchaser, shall be the sole responsibility of the
purchaser. WARRANTY SERVICE is at the sole discre-
tion of Comptus and free of charge for parts and labor.
Under the above terms, Comptus will repair or replace the
defective component(s), provided that:
a) the product has not been subjected to abuse, neglect,
accident, alteration, improper installation or servicing, or
used in violation of instructions furnished by Comptus;
b) the product has not been repaired or altered by anyone
except Comptus or its authorized service agencies;
c) the serial number has not been defaced, removed, or
otherwise changed;
d) the damage has not been caused by acts of nature
including windstorm and hail beyond those specified as
within the range of operating conditions;
e) the damage has not been caused by shipping.
THIS WARRANTY IS IN PLACE OF ALL OBLIGA-
TIONS OR LIABILITIES ON THE PART OF
COMPTUS FOR DAMAGES. IT DOES NOT APPLY
TO ANY COMPONENT OR EQUIPMENT RESOLD
BY COMPTUS IN ITS ORIGINAL CONDITION AS
RECEIVED BY COMPTUS FROM THE MANUFAC-
TURER OR DISTRIBUTOR, AMONG THE DAM-
AGES EXCLUDED FROM THIS WARRANTY ARE
ANY INCIDENTAL OR CONSEQUENTIAL DAM-
AGES ARISING OUT OF OR IN CONNECTION
WITH THE PRODUCT IN ANY WAY. Any implied
warranties are limited in duration to the duration of
the written warranty. No representative or person is
authorized to give any other warranty or assume for
Comptus any other liability in connection with the sale
of its products.
THIS WARRANTY GIVES YOU SPECIFIC LEGAL
RIGHTS, AND YOU MAY ALSO HAVE OTHER
RIGHTS WHICH VARY FROM STATE TO STATE.
SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF INCIDENTAL OR CONSEQUEN-
TIAL DAMAGES OR LIMITATIONS ON HOW LONG
AN IMPLIED WARRANTY LASTS, SO THE ABOVE
LIMITATIONS AND/OR EXCLUSIONS MAY NOT
APPLY TO YOU. This warranty complies with the
Magnuson-Moss Consumer Warranty Act, and completely
replaces any warranty printed on promotional material
describing products of Comptus Inc.
.HOW TO RETURN EQUIPMENT
TO COMPTUS
1. Contact the Comptus Service department with the
model and serial number of the unit. Be prepared to
provide the symptoms of the problem as many are solved
without the need for returning the equipment. Have a
person with firsthand experience of the trouble on hand to
provide specific information.
2. Comptus will issue a Return Material Authorization
Number (RMA#) if required. This will ensure the fastest
response and least cost for all parties. Please reference this
number in all correspondence. This number should be
printed on the shipping container.
3. Include a description of the service desired with the
returned equipment. If the equipment is being returned for
repair, please include a description of the problem.
4. If the equipment is packaged in a plastic case, wrap it in
aluminum foil, or other conductive material. This will
protect it from static electricity, as well as prevent the
packing material from jamming mechanical parts, such as
switches. Otherwise, place the equipment in a plastic bag,
again to prevent contamination by packing material.
Place the equipment in a suitable shipping container and
fill with packing material. There should be at least one
inch of packing material between the equipment and the
shipping container on all sides.
5. Equipment will be returned C.O.D. to sender if any
charges are incurred, unless other arrangements are made
in advance.
SHIP THE EQUIPMENT TO:
Comptus Inc.
342 Lyndeboro Rd.
New Boston NH 03070 U.S.A.
Telephone : [phone]
Telfax : 603 487-5513
e-mail : [email protected]
NOTE: Please be sure to include the RMA Number, as
described in Item 1, on the shipping container.

12
342 Lyndeboro Rd., New Boston, NH USA
Phone: [phone] Fax: [phone] E-mail: [email protected]
Comptus Inc
ISO 9001 Registered ®

13
A70-RL
Packing List
Qty. Description
1 A70-RL Rain gage Transmitter
1 Rain gage
1 Instruction Manual
1 Certificate of Calibration
—
342 Lyndeboro Rd., New Boston, NH USA
Phone: [phone] Fax: [phone] E-mail: [email protected]
Comptus Inc
ISO 9001 Registered ®
IMPORTANT: Please check your order on re-
ceiptto be certainalllisted accessories areincluded
before discarding shipping container or packing
material. All shortages must be reported within
10 days of receipt.

14
342 Lyndeboro Rd., New Boston, NH USA
Phone: [phone] Fax: [phone] E-mail: [email protected]
Comptus Inc
ISO 9001 Registered ®