Campbell Scientific Q7-1-L User Manual

INSTRUCTION MANUAL

Q-7.1 Net Radiometer

Revision: 5/96

Copyright (c) 1991-1996

Campbell Scientific, Inc.

Warranty and Assistance

The Q-7.1 NET RADIOMETER is warranted by CAMPBELL SCIENTIFIC,
INC. to be free from defects in materials and workmanship under normal use
and service for twelve (12) months from date of shipment unless specified
otherwise. Batteries have no warranty. CAMPBELL SCIENTIFIC, INC.'s
obligation under this warranty is limited to repairing or replacing (at
CAMPBELL SCIENTIFIC, INC.'s option) defective products. The customer
shall assume all costs of removing, reinstalling, and shipping defective products
to CAMPBELL SCIENTIFIC, INC. CAMPBELL SCIENTIFIC, INC. will
return such products by surface carrier prepaid. This warranty shall not apply
to any CAMPBELL SCIENTIFIC, INC. products which have been subjected to
modification, misuse, neglect, accidents of nature, or shipping damage. This
warranty is in lieu of all other warranties, expressed or implied, including
warranties of merchantability or fitness for a particular purpose. CAMPBELL
SCIENTIFIC, INC. is not liable for special, indirect, incidental, or
consequential damages.

Products may not be returned without prior authorization. The following
contact information is for US and International customers residing in countries
served by Campbell Scientific, Inc. directly. Affiliate companies handle repairs
for customers wi thin their territories. Please visi t www.campbellsci.com to
determine which Campbell Scientific company serves your country. To obtain
a Returned Materials Authorization (RMA), contact CAMPBELL
SCIENTIFIC, INC., phone [phone]. After an applications engineer
determines the nature of the problem, an RMA number will be issued. Please
write this number clearly on the outside of the shipping container.
CAMPBELL SCIENTIFIC's shipping address is:

CAMPBELL SCIENTIFIC, INC.

RMA#_____
815 West 1800 North
Logan, Utah 84321-1784

CAMPBELL SCIENTIFIC, INC. does not accept collect calls.

Q-7.1 NET RADIOMETER

The Q-7.1 is a high-output thermopile sensor which measures the algebraic sum of incoming and
outgoing all-wave radiation (i.e. short-wave and long-wave components). Incoming radiation consists of
direct (beam) and diffuse solar radiation plus long-wave irradiance from the sky. Outgoing radiation
consists of reflected solar radiation plus the terrestrial long-wave component.

1. SPECIFICATIONS

• 60-junction thermopile with low electrical
resistance (4 ohms nominal) to reduce
susceptibility to noise

• Nominal calibration factors 9.6 W m
(for positive values), 11.9 W m
negative values)

• Spectral response 0.25 to 60 µm

• Uncorrected wind effect: up to 6%

reduction @ 7 m s
to 1% reduction @ 7 m s

-1

for positive fluxes, up

-1

for negative

fluxes.

-2

mV

-2 mV-1
1

-

(for

CAUTION: Ensure that the cable is tied to
the support arm close to the ball joint. If
the wires are allowed to flex where they
emerge from the sensor head they will
break. Sensors are shipped with an
appropriate cable tie already installed.

• Time constant: Approximately 30 seconds

• Top and bottom surfaces painted black and

protected from convective cooling by
hemispherical heavy-duty polyethylene
windshields (0.25 mm thick)

• Windshields do not require pressurization

• O-ring seals for easy windshield

replacement

• Desiccant contained in support arm;
volume of desiccant tube 45 cm

3

; breather

port on the end of the support arm.

• No power required

• Size of sensing head 57 x 72 x 177 mm;

support arm 20 mm diameter, 750 mm long

2. INSTALLATION

Attach the square mounting plate to a vertical or
horizontal pipe or rod that is less than 38 mm
(1.5 inches) in diameter with the two larger U­bolts. Attach the radiometer support arm to the
mounting plate with the two smaller U-bolts.
The radiometer support arm does not need to be
level. Fasten the cable to the pipe or rod with
tape or plastic ties to prevent strain on the wires
and damage to the instrument.

In the northern hemisphere install the
radiometer so that the sensor head is pointing
south. Likewise, in the southern hemisphere
point the sensor head to the north.

2.1 LEVELING

The Q-7.1 must be level. The bubble level is
accurate to ±1° and the bubble should be within
the bulls-eye. An error of 5° in leveling may
cause a cosine response error of 6% under
normal conditions; much greater errors are
possible under other conditions (e.g. sunrise,
sunset and winter use with low sun angles).

To level the Q-7.1, use a 5/8" wrench on the
hexagonal coupling nut on the instrument stem
to bend the ball joint between the support arm
and the instrument. If the instrument does not
stay in position, tighten the large hexagonal nut
on the support arm slightly with a 15/16"
wrench.

CAUTION: Do not attempt to bend the ball
joint by holding the instrument head alone,
as this may break the stem.

1

Q-7.1 NET RADIOMETER

2.2 WIRING

If a differential measurement is made, connect
the red (+) lead to the high side (e.g. 1H) of any
datalogger differential channel and the black (-)
lead to the low side (e.g. 1L). Also, connect a
jumper wire between the low channel and
analog ground to prevent common mode
errors. Connect the clear (shield) lead to
ground (G on the CR10(X), ground on the 21X
and CR7).

If a single-ended measurement is made,
connect the red lead to any datalogger single­ended channel (H or L) and the black lead to
ground (AG on the CR10(X), ground on the 21X
and CR7).

The black lead is negative with respect to the
red lead when the net radiometer is mounted
with the level up and there is more incoming
radiation than outgoing.

3. PROGRAMMING

Measure the output of the Q-7.1 with either
Instruction 2 (Differential Volts) or Instruction 1
(Single-Ended Volts). Use the 250 mV range
for the CR10(X) and the 500 mV range for the
21X or CR7. The slow integration with 60 Hz
rejection yields a more noise-free reading.

For still air, net radiation (Q*) can be computed
from the thermopile voltage (V

If V

> 0, Q*(Wm-2) = Vt(mV) x F

t

If Vt < 0, Q*(Wm-2) = Vt(mV) x F

) by:

t

p
n

where Fp and Fn are the positive and negative
calibration factors respectively.

The calibration factors and serial number are
given on a label under the sensor head.

The above formula give the correct readings
for conditions of zero wind speed. Additional
corrections can be applied to reduce errors for
non-zero wind speeds.

3.1 CORRECTING ERRORS CAUSED BY WIND EFFECT

Most sensors which measure long wave
radiation are subject to some degree of error
caused by convective cooling as air moves
past the sensors. The response of the Q-7.1
sensor has been determined by the
manufacturer using a specially constructed
wind tunnel. Curves fitted to experimental data
by the manufacturer are given in Figure 1.
These functions show the change in reading in
response to increasing wind speed.

FIGURE 1. Percentage Change in Reading as a Function of Wind Speed

2