Buck 1011C User manual

MODEL 1011C HYGROMETER
OPERATING MANUAL
December 2008
BUCK RESEARCH INSTRUMENTS, LLC
PO Box 19498
Boulder, CO 80308
Copyright 2008. Buck Research Instruments, LLC All rights reserved.

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TABLE OF CONTENTS
1.0 INTRODUCTION p.5
1.1 General Operational Description
1.2 Brief Physical Description
1.3 Specifications
1.4 List of improvements from the 1011B
1.5 Acknowledgment
2.0 CONTROLS, CONNECTORS, AND MAJOR COMPONENTS p.11
2.1 Sensing Unit
2.2 Control/Indicator Unit
2.3 Power Unit
2.4 Cables
2.5 Optional Accessories
3.0 INSTALLATION
p.18
3.1 Unpacking Procedure
3.2 Initial Operation Check
3.3 Installation on Aircraft
3.4 Leak Check
3.5 Pressure Within Sensor
3.6 Cabling
4.0 OPERATING INSTRUCTIONS p.24
4.1 Initial Setup
4.2 System Operation
4.2.1 Time Response
4.2.2 Mirror Cleanliness
4.2.3 Supercooled Dew Points
4.2.4 Low Frost Points
4.2.5 Pressure Effects
4.2.6 Typical Response to Humidity Changes
4.2.7 Mirror Flooding
4.3 Operation while Parked or off the Aircraft
5.0 PREVENTIVE MAINTENANCE AND TROUBLESHOOTING p.29
5.1 Periodic Inspection
5.2 Cleaning System Optics

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FIGURES
Number Title
1 Model 1011C Dew Point Hygrometer System p.7
2Depression capability p.9
3Dew Point Sensing Unit p.12
4 Control/Indicator Unit p.14
5 Power Unit, External p.15
6 Power Unit, Internal p.17
7 Sensing Unit: Mounting and Assembly p.20
8 Sensing Unit, Internal p.22
9 Flow Test Fixture Hookup p.23
10 System Response Characteristics p.28
Appendix Figures:
11. 1011C Wiring Diagrams p.31-2
12 Water Vapor Conversions p.33
13 Vapor pressure vs. dew/frost point p.34
14 Absolute humidity vs. dew/frost point p.35
15 Effect of pressure on dew point p.36
16 Aspirating Fixture Hookup p.37
17 1011C Hygrometer Complete p.38

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LIST OF TABLES
Number Title
1 1011C Connectors p.39
2 Dew Point to Frost Point Conversions p.40
3 Dew Point Error Due to Pressure Change in Sampling System p.41
APPENDIXES
1 1011C Pin Out p.30
2 Humidity Conversion Equations p.42
3 Warranty p.44

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SECTION 1. INTRODUCTION
1.1 GENERAL OPERATIONAL INSTRUCTIONS
The 1011C is a high performance condensation type hygrometer designed for airborne
measurement of dew and frost point temperatures. The system is capable of measuring
dew/frost points between -75°C and +50°C, over a wide range of temperatures, pressures,
and airspeeds. The 1011C is a complete update of the 1011B hygrometer, incorporating
many new features described below.
The instrument operates on the chilled-mirror principle. A mirror is thermoelectrically
cooled until it reaches a temperature at which condensation begins to form (the dew or
frost point), and is then held at that temperature; the presence of condensation is sensed
optically. The signal output is a voltage corresponding to the temperature of the mirror.
The 1011C consists of three distinct units – a Sensor unit, a Power unit and a
Control/Indicator unit. The Sensor unit contains a three-stage thermoelectric cooler (TEC)
capable of reaching frost points normally encountered at altitudes up to 45,000 feet.
ALL PARTS OF THE 1011C CAN ONLY BE USED WITH THE 1011C. NONE OF
THE 1011B COMPONENTS CAN BE INTERCHANGED WITH THE 1011C.
The 1011C features a microcontroller-based Power unit. It features both voltage and 9600
baud RS-232 serial data outputs. Optionally, it includes a power switch and a pressure
sensor input.
The Control/Indicator unit features LEDs that indicate mirror cleanliness, an LED display
that shows dew/frost point temperature, and a blue LED that indicates whether the
instrument is controlling on a dew or a frost point.
The instrument will operate well in most environments, both on and off aircraft. Although
the standard configuration is designed for in-flight operation, an optional aspirating kit
enables use while the aircraft is on the ground, as well as off the aircraft in a lab or other
environment.
Startup and operation are normally very simple. Excluding extreme humidity
environments, no in-flight adjustments are required.
Note: An aircraft is an exceedingly difficult platform from which to make
humidity measurements, because of the extreme range of environmental
conditions which can occur, the abruptness of changes encountered, and
various thermodynamic and aerodynamic considerations. While the 1011C
is designed using the highest standards in this type of instrument, in-flight
situations can be encountered which will tax its limits. To help assure
consistently good performance, a number of cautionary factors are
discussed in this manual.

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1.2 BRIEF PHYSICAL DESCRIPTION
Physically, the system (Figure 1) consists of a sensing unit, a control/indicator unit, a
power unit, associated cabling, and a maintenance unit.
The Sensing Unit (A) is the moisture-detecting device. It contains a right or left hand inlet
fitting, a mirror, sensing/control optics, a thermistor, a TEC, and associated electronics.
The Control/Indicator Unit (B) is the user interface component, and contains the on/off
function switch, balance control, and displays.
The Power Unit (C) distributes operating power to the system components and contains the
circuitry that controls the thermoelectric cooler and converts mirror temperature to a
suitable output signal (provided at rear of unit). The unit is equipped with quick-remove
shock mount.
The Maintenance kit: Consisting of bottles for water and acetone, cotton swabs and spare
gaskets and o-rings. Unlike the 1011B, the 1011C does not come with a calibration plug.
This is because the 1011C uses an ultra-stable thermistor instead of an RTD, which
improves speed of response and is far less susceptible to drift. Additionally, the
temperature is measured with an analog-to-digital converter (ADC) that is calibrated each
time the instrument is turned on and is not susceptible to drift like the analog electronics in
the old 1011B instrument, and therefore does not need a calibration plug.
Three Cables or six Connectors, a Data Connector, and a Power Connector connect the
various system components and provide input power.
Optional Accessories, which further increase versatility and ease of use, are described in
Section 2.6.
Note:The 1011B hygrometer was originally developed and produced by
General Eastern Instruments. This operating manual originated at General
Eastern, and many of the drawings are reproduced by their courtesy.

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C
B
A
Figure 1. Dew Point Hygrometer System
(shown with optional cables)

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1.3 SPECIFICATIONS
Dew point range: -75 to +50 °C nominal
(see also Figure 2)
Accuracy ± 0.1° C RS-232
± 0.3° C LED display
Response time: Variable
(see Sect. 4.2.1)
OutputsAnalog:
Dew point: 0.08 v/°C, 6v = 0°C
Control voltage: 0 – 10 vdc
Minimum load impedance 5 K ohms
Digital display resolution: 0.1 °C
Power Input 28 vdc, 2.5 A max
Operating Limits
Operating temperature range
Sensing Unit: -80 to +60 °C
Control/Indicator Unit: -40 to +60 °C
Power unit: -40 to +60 °C
Airspeed (nominal): 450 knots
Altitude (nominal): 45,000 feet
Pressure Limit: 1.5 atmospheres
Dimensions in inches
Sensing Unit
Diameter (max): 2.50
Length (with inlet fitting): 4.25
Control/Indicator unit
Height: 3.26
Width: 3.26
Depth: 5.88
Power unit, including shock mount
Height: 6.38
Width: 6.06
Depth: 12.0
Weight, lbs.
Sensor: 1.5 lbs.
Control/Indicator: 1.25 lbs.
Power unit: 3.25 lbs.
Cables: 8.0 oz.

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1.4 NOTE TO USERS OF 1011B SYSTEMS
The following is a list of improvements made:
1. 28 VDC operation.
2. RS-232 data output
3. Improved accuracy, ± 0.1 degree C over entire range*
4. Improved servo control, reducing oscillations be a factor of 10.
5. Improved cooling of at least 10 degrees C
6. Faster and more accurate response at low dew points
7. Software-upgradeable by end user.
8. Optional pressure sensor input and mixing ratio output
9. Autobalance feature automatically compensates for reduced mirror reflectivity
caused by contamination.
10. Service Mirror LED illuminates to indicate mirror contamination is too great
and mirror needs to be cleaned.
11. D/F Point LED, which illuminates when a dew or frost point is reached
*RS-232 output only
1.5 ACKNOWLEDGMENT
David M. McFarland at the National Center for Atmospheric Research initially developed
the flow test fixture and the aspirating fixture. We acknowledge with appreciation Mr.
McFarland's contribution in making these devices available to the user community.

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SECTION 2. CONTROLS, CONNECTORS, AND MAJOR COMPONENTS
2.1 SENSING UNIT (Figure 3)
A. Inlet Fitting - has inlet, exhaust, and water drain ports. Each fitting is designed for use
on either the left or the right side of the aircraft, but not for both.
B. Mounting collar. The mounting collar has 6 holes drilled in it that are ready to be
tapped for either 8-32 or M4 screws for mounting. Buck Research Instruments, LLC
does not tap these holes unless specifically requested by the customer, as mounting
configurations and requirements vary from aircraft to aircraft.
C. Connector (J6) - for cable leading to power unit.

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Figure 3. Dew Point Sensing Unit
A
B
C

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2.2 CONTROL/INDICATOR UNIT (Figure 4)
A. Function switch (S1) - applies power to the various system supplies, and provides
the following functions:
OFF - no power applied to any circuit.
DEW POINT - normal operating position. Allows system to maintain an
equilibrium condensation layer on the mirror.
BAL - heats the mirror to 40° C to evaporate condensation. Allows system
to be balanced with a dry mirror. Do not leave in this position once balance
routine is initiated or it will repeatedly balance mirror. Switch back to DEW
POINT position once REBALANCE LED lights
MAX COOL – switch position that applies full cooling current to the
thermoelectric cooler. This is used to (1) determine whether there is
adequate cooling when the system is operating at very low frost points, and
(2) convert any supercooled water deposit to frost.
B. Digital Panel Meter (M1) – allows direct readout of dew point data.
C. D/F Point LED - blue LED indicates if unit has stabilized on a dew or frost point.
D. REBALANCE LED. Lights when a balance routine is performed. If it stays light
after balance finishes, this indicates that mirror is becoming contaminated and will
need to becleaned soon.
E. SERVICE MIRROR LED. This LED flashes to indicate that mirror is too
contaminated for proper operation and needs to be cleaned.
F. Main Connector J8 - for cable leading to control unit.

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Figure 4. Control/Indicator Unit
F
A
B
C
D
E

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2.3 POWER UNIT (Figure 5)
A. SENSOR Connector (J5) - for cable to sensor.
B. CONT/IND Connector (J7) - for cable to Control/Indicator.
C. DATA OUT Connector (J4) - provides analog signal outputs.
D. POWER IN Connector (J1) - for connecting +28 VDC.
E. PRESSURE – to connect to optional pressure sensor
F. RS-232—serial data output (9600 Baud 8-N-1)
The power unit is no longer furnished with a shock-mounted base as we have determined
that one should not be required for most aircraft installations. If shock mounts are deemed
necessary, they are made by Barry Controls and the part number is Barrymount L44-
BA(M)-2. (Use BAM for metric and BA for standard). Install one on each corner of the
Power unit using the screw holes on the blue mounting brackets on the bottom. You will
need a total of 4 Barrymounts.
Figure 5. Power unit.

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2.4 CABLES
Six connectors and wiring diagrams or three cables are supplied: power unit to
+28 VDC, power unit to sensing unit, and power unit to control/indicator unit.
Each connector is unique, so that it is impossible to accidentally connect the cables
incorrectly.
2.5 OPTIONAL ACCESSORIES
Aspirating Kit. Provides airflow through the 1011C sensor when it is not exposed
to in-flight conditions. It consists of an aspirating fixture which attaches to the
sensor, a pump, a floating ball flowmeter with control valve, and a length of non-
hygroscopic tubing with fittings.
The fixture attaches itself quickly and allows an operational check of the entire
system in the lab or on the aircraft while parked. It also allows use of the
system in the lab or other off-aircraft environments, and permits a complete leak
check to be performed.
Inlet Fitting. Spare to allow choice of right side or left side operation.

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Figure 6. Power Unit, Internal

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SECTION 3. INSTALLATION
3.1 UNPACKING PROCEDURE
1. Remove system components from shipping containers and situate near a 28 VDC
power source. If possible, save shipping containers for future use.
2. Make sure that all system components are accounted for (Figure 1).
3. Ascertain they are properly matched by serial number, or have been calibrated
together.
4. Visually inspect exterior of system components and interconnecting cables for
damage. If damage is evident take appropriate action for corrective maintenance
and repair, as required.
5. Record serial numbers.
3.2 INITIAL OPERATIONAL CHECK
Before mounting on the aircraft, it is advisable to give the system an initial bench
check to verify that it works properly and to become familiar with its operation.
See Section 4.3 for operation off the aircraft.
3.3 INSTALLATION ON AIRCRAFT
Sensing unit
The sensor is normally located on the aircraft fuselage, mounted through the exterior skin,
with the inlet fitting exposed to the airstream. Other locations, such as a boom, can also be
used.
The pressure field along the side of an aircraft in flight varies with location, and may be
greater or less than the ambient or static pressure. Attempt to locate the sensor at a point
where the pressure is reasonably near static pressure. A side mount is advisable to avoid
pressure changes with change of aircraft pitch, and to avoid rain while parked. Avoid prop
wash and areas of large local pressure changes, such as wing surfaces, behind radar domes
and struts, etc. It is usually safe to mount the sensor near the static instrument ports, as
they are located at or near a point of static pressure.
In pressurized aircraft, try to avoid locating immediately downstream of windows or other
cabin penetrations that might have slight leaks and thereby affect the air being sampled. A
forward location allows a somewhat better penetration of the aircraft boundary layer by the probe,
and so is somewhat preferable (although usually not critical).
The inlet fitting is designed for use on either the right or the left side of the aircraft, but not
both. The consequence of mounting on the wrong side of the aircraft is: upward pointing
inlet and exhaust holes and the likelihood of collecting liquid water in the sensor.

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The sensor should be mounted as shown in Figure 7. Initially, orient the sensor so the inlet
fitting points downstream, parallel to the airstream, with the inlet and exhaust holes
pointed downwards. As soon as practical, adjust for proper flow and pressure change in
the cavity, according to Section 3.5.
Power Unit
Wire up cables and connect the proper cables (they are coded to prevent mismatch).
+28VDC must be used. Using any other power will damage the unit and void the warranty.
Control/Indicator Unit
If practicable, mount so that the front panel is accessible during flight. Make sure function
switch S-1 is in OFF position. Connect cable.
Cable Length
Standard cable lengths may be extended as follows on special order:
Sensing unit to power unit: 3 feet (1m) standard, may go to 50 feet.
Control/Indicator to power unit: 3 feet (1m) standard, may go to 150 feet.
It is essential that cables be identical in quality and configuration to that of original
equipment or the cable specified in the drawings. Specifically, that there are 7 pairs of
shielded 24 gauge wires and 2 pair of shielded 18 gauge wires contained in the cable used
for connecting between the power unit and the control/indicator unit and the cable used for
connecting the power unit to the sensor unit. It would also be acceptable to make a cable
using 9 separate cables that are shielded, twisted-pair (7 of them 24 gauge and 2 of them
18 gauge) and wrapping them together Make sure that there is an overall, braided shield
surrounding these cables and attached at both ends to the connector. Use of non-standard
cable may cause operational problems and make the unit more susceptible to noise and
electrostatic discharge.
Sensor Body Temperature
There is a trade-off involved in the degree to which the sensor body is thermally coupled to
the outside ambient temperature. If it is held closely to outside temperature, the
thermoelectric cooler will have the lightest cooling load, and the instrument will be able to
achieve maximum performance at very low frost points (high altitudes); it may, however,
become flooded on descent when the cold sensor body suddenly encounters warm moist
air. If on the other hand, the sensor body is strongly influenced by the heated cabin, the
reverse will be true: better stability on descent, but reduced performance at frost points
below -50° C. In practice, normal mounting on

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Figure 7. Sensing Unit: Mounting
Note: #6-32 screws go into the mount collar, which has a maximum depth of 0.375”. Add this length to the
total thickness of the aircraft skin and any plates used to deternine screw length.