INSTRUCTION MANUAL
0871LH1
Freezing Rain Sensor
November 2012
Copyright © 2007
Campbell Scientific (Canada)Corp.
TABLE OF CONTENTS
Purpose .............................................................................................................................................. 2
1
2 General ............................................................................................................................................... 2
3 Detailed Principle of Operation ........................................................................................................... 2
4 Specifications ..................................................................................................................................... 4
5 Physical Description ........................................................................................................................... 5
6 Temperature Considerations .............................................................................................................. 6
7 Power Interruptions ............................................................................................................................ 6
8 Mounting Considerations ................................................................................................................... 6
9 Wiring ................................................................................................................................................ 7
9.1 0871LH1CBL-L Wiring for Discrete Output ............................................................................... 7
9.2 0871LH1CBL-L Wiring for RS422 Output ................................................................................. 8
10 Program Examples .............................................................................................................................. 9
10.1 CR1000 Example – Discrete Outputs ....................................................................................... 9
10.2 CR23X Example – Discrete Outputs ....................................................................................... 10
10.3 CR1000 Example – RS422 Outputs ........................................................................................ 11
Appendix A:
1
RS-422 Output Format for non-Campbell Datalogger Applications ................................................... 17
2 Built In Test (BIT) ............................................................................................................................... 17
3 Hardware Built-In-Test (BIT) .............................................................................................................. 17
4 Continuous Built-In-Test (BIT) ........................................................................................................... 17
5 BIT Failure That Disables Ice Output .................................................................................................. 18
6 Operator-Initiated Tests .................................................................................................................... 19
7 Initiated Built-In-Test (BIT) ................................................................................................................. 19
8 Correlation Counting ........................................................................................................................ 20
9 Ice Detector RS-422 String Format .................................................................................................... 21
10 Electrostatic Discharge (ESD) Consideration ...................................................................................... 22
Appendix B:
Freezing Rain Sensor Block Diagram ................................................................................................. 23
1
1.1 Microcontroller ......................................................................................................................... 24
1.2 Watchdog/Reset Circuit ........................................................................................................... 24
1.3 Serial EEPROM ....................................................................................................................... 24
1.4 Probe Oscillator ....................................................................................................................... 24
1.5 Heater Control ......................................................................................................................... 24
1.6 Drive Coil ................................................................................................................................. 25
1.7 Feedback Coil ......................................................................................................................... 25
1.8 Heater ...................................................................................................................................... 25
1.9 DC Power Supply .................................................................................................................... 25
1.10 Status Output .......................................................................................................................... 25
1.11 Ice Signal Output ..................................................................................................................... 25
2 Qualification Capabilities .................................................................................................................. 26
3 Input/Output Specification ............................................................................................................... 27
3.1 Input/Output Pin Designations ................................................................................................. 27
TABLE OF FIGURES
Figure 1 MSO Circuit Sectional View .............................................................................................................................................. 3
Figure 2 MSO Circuit Schematic ...................................................................................................................................................... 3
Figure 3 Ice Detector ............................................................................................................................................................................ 5
Figure 4 Mounting (part number 0871LH1 MNT) .................................................................................................................... 6
Figure 5 General Hook-up Diagram ............................................................................................................................................... 8
Figure 6 Functional Block Diagram ............................................................................................................................................. 23
1
1 Purpose
This document provides detailed information about the Rosemount
Aerospace model 0871LH1 Freezing Rain Sensor for use in ground-based
meteorological applications. Topics covered include requirements,
qualification categories and methodology, and detailed design
information.
2 General
The Rosemount Aerospace 0871LH1 Freezing Rain Sensor is a one-piece
unit that detects the presence of icing condition. Twenty-four volts DC
input power is provided to the freezing rain sensor. The freezing rain
sensor outputs include ice detection indication and fault status
indication. These outputs are provided through an RS-422 interface and
discrete outputs. One freezing rain sensor is used on each station and
provides the primary means of ice detection. The ice signal is used to
indicate to the operator that an icing condition exists so that appropriate
actions can be taken.
3 Detailed Principle of Operation
The freezing rain sensor uses an ultrasonically axially vibrating probe to
detect the presence of icing conditions. The sensing probe is a nickel
alloy tube mounted in the strut at its midpoint (node) with one inch
exposed to the elements. This tube exhibits magnetostrictive properties:
it expands and contracts under the influence of a variable magnetic field.
A magnet mounted inside the strut and modulated by a drive coil
surrounding the lower half of the tube provides the magnetic field.
A magnetostrictive oscillator (MSO) circuit is created with the above
components and the addition of a pickup coil and an electronic
comparator. The ultrasonic axial movement of the tube resulting from
the activation of the drive coil causes a current to be induced in the
pickup coil. The current from the pickup coil drives the comparator that,
in turn, provides the signal for the drive coil.
The oscillation frequency of the circuit is determined by the natural
resonant frequency of the sensor tube, which is tuned to 40 kHz. With the
start of an icing event, ice collects on the sensing probe. The added mass
of accreted ice causes the frequency of the sensing probe to decrease in
accordance with the laws of classical mechanics. A 0.5mm (0.020”)
thickness of ice on the probe causes the operating frequency of the
probe to decrease by approximately 130 Hz. The freezing rain sensor
onboard software monitors the probe frequency, detects and
annunciates any frequency decrease. At the same time, the internal
probe heater power is applied until the frequency rises to a
predetermined set point plus an additional delay factor to assure
complete de-icing.
Once de-iced, the sensing probe cools within a few seconds and is ready
to sense ice formation again. When ice forms on the sensing probe again
to the point where the MSO frequency decreases by 130 Hz, the sensor
de-ices itself again. This cyclic process is repeated as long as the freezing
2
rain sensor remains in an icing environment. The ice signal activates at
0.5mm ice accretion and stays on for 60 seconds after the end of the icing
encounter. Specifically, when the output is activated, a 60-second timer is
started. Each time 0.5mm forms on the probe, the 60-second counter is
reset. In effect, the output stays on for 60 seconds after the beginning of
the “last” icing encounter.
The Status output indicates whether the freezing rain sensor is
functioning correctly using tests that are described in more detail in
following sections of this document.
Ultrasonic Vibrating Probe
Ultrasonic Vibrating Probe
40KHz Nominal
40KHz Nominal
Drive Coil
Drive Coil
Feedback Coil
Feedback Coil
Magnet
Magnet
Probe Heater
Probe Heater
Termination
Termination
Figure 1 MSO Circuit Sectional View
Strut Heaters
Strut Heaters
Figure 2 MSO Circuit Schematic
3
4 Specifications
Power Supply
Operating Voltage: 18 – 29.5 VDC
Power Draw: 5W max at 24 VDC (sensing mode)
27W max at 24 VDC (deicing mode)
Temperature
Operating: -55°C to +71°C
Storage: -65°C to +90°C
Communication Outputs
Discrete Outputs: for Icing and Status
No Icing – Open, Icing – Ground
Status OK – Ground, Status Failure – Open
RS-422: Hexidecimal 24-byte string (ASCII format)
9600 Baud (1 Start Bit, 8 Data Bits, No Parity, 1
Stop Bit)
RS422 Outputs: for Icing and Status
No Icing – 0, Icing – 1
Status OK – 0, Status Failure – 1
Icing Signal Period: 60 second activation from start of icing
measurement (Discrete or RS-422 outputs)
Connector Pinout
Table 1. 0871LH1 Connector Pinout
Connector Pin Signal Description
A 24VDC
B 24VDC Return
C Case Ground
D RS-422 High
E RS-422 Low
F Ice
G Status
Mating Connector: MS27473T10B99SN
De-icing Control Automatically triggered with accumulation of
0.5mm of ice on probe
Max heating time – 25 seconds
4
5 Physical Description
The freezing rain sensor is an integrated unit containing both the sensor
and processing electronics. It contains a 7.35 cm (2.9”) square faceplate
for mounting to the 0871LH1MNT and a 7.28 cm (2.86”) diameter housing
containing the processing electronics. The maximum weight of a unit is
318 grams (0.7lbs).
Figure 3 Ice Detector
5
6 Temperature Considerations
In the case of unit malfunction causing strut heater lock-on, the probe
temperature can exceed 204.4°C. Maintenance personnel should exercise
caution when servicing the unit.
7 Power Interruptions
The freezing rain sensor is qualified to DO-160C power input category Z.
The unit will remember status through a 200 ms power interruption, but
the output string will cease during the interruption.
The freezing rain sensor uses a power fail monitor to verify the supply
voltage. If a power fault is detected the freezing rain sensor is halted with
a failure indication on the STATUS discrete output.
8 Mounting Considerations
Figure 4 Mounting (part number 0871LH1 MNT)
The freezing rain sensor should be mounted to a sturdy crossarm located
away from buildings or other obstacles that could shadow the sensing
element from freezing rain. The sensor should be installed so that the
sensing probe is a minimum of 92cm (36”) above the ground.
1. Remove the protective tube from strut.
2. Attach the freezing rain sensor to the mounting bracket using the
supplied ¼ - 20 screws and lock washers. Position the freezing rain sensor
on the mounting pole with the sensing probe pointing upward, with the
bracket inclined at a 20° - 30° angle above horizontal to ensure proper
drainage of melted ice.
3. Attach to a vertical or horizontal pipe using the supplied V bolts, nuts and
washers. NOTE: The sensor should be mounted so as to be oriented into
the prevailing wind.
4. Connect cable to 0871LH1 connector and secure cable to bracket with
cable ties.
5. Remove shipping cover and protective cap prior to powering on the unit.
6
9 Wiring
0871 LH1C BL-L Wiring for Discrete Output
The wiring of the 0871LH1 will depend on the required communication
outputs of your application. If you require the use of the discrete outputs
of the 0871LH1, then refer to section 9.1. If you require the use of the RS422 output, then refer to section 9.2.
NOTE:
9
Please contact a Certified Electrician to properly install the C2673 power
supply. All electrical connections and housings must be installed by a
Certified Electrician.
Table 2. Datalogger Connections
Description Pin Colour CR3000/CR1000 CR10X/CR510
Ice F Blue C1 C1
Status G Yellow C2 C2
RS422 A D White N/C N/C
RS422 B E Brown N/C N/C
Power Reference B Black G G
Case GND C Green G G
5V Power Purple 5V 5V
Shield Clear G G
WARNING:
WARNING:
7
The 5VDC connection must be made to avoid damage to the 0871LH1.
Isolate wires that are not connected as they will cause problems if shorted
to ground.
Table 3. Power Connections to Terminal Expander
Description Pin Colour Connection
24VDC A Red V+
24VDC Return B Black V-