Campbell 0871LH1 User manual

INSTRUCTION MANUAL
Copyright © 2007
Campbell Scientific (Canada)Corp.
0871LH1
Freezing Rain Sensor
December 2008

WARRANTY AND ASSISTANCE
This equipment is warranted by CAMPBELL SCIENTIFIC (CANADA) CORP. (“CSC”) 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
are not warranted. ***** CSC's obligation under this warranty is limited to repairing or
replacing (at CSC's option) defective products. The customer shall assume all costs of
removing, reinstalling, and shipping defective products to CSC. CSC will return such
products by surface carrier prepaid. This warranty shall not apply to any CSC 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. CSC is not
liable for special, indirect, incidental, or consequential damages.
Products may not be returned without prior authorization. To obtain a Return
Merchandise Authorization (RMA), contact CAMPBELL SCIENTIFIC (CANADA) CORP.,
at [phone]. An RMA number will be issued in order to facilitate Repair Personnel
in identifying an instrument upon arrival. Please write this number clearly on the outside
of the shipping container. Include description of symptoms and all pertinent details.
CAMPBELL SCIENTIFIC (CANADA) CORP. does not accept collect calls.
Non-warranty products returned for repair should be accompanied by a purchase order to
cover repair costs.

TABLE OF CONTENTS
1 Purpose .................................................................................................................................3
2 General..................................................................................................................................3
3 Detailed Principle of Operation............................................................................................3
4 Physical Description.............................................................................................................6
5 Temperature Considerations.................................................................................................6
6 Power Interruptions ..............................................................................................................6
7 Mounting Considerations......................................................................................................7
8 Wiring Diagram....................................................................................................................8
9 Program Examples................................................................................................................9
9.1 CR23X..........................................................................................................................9
9.2 CR1000.......................................................................................................................10
APPENDIX A
1 RS-422 Output Format for non-Campbell Datalogger Applications..................................12
2 Built In Test (BIT)..............................................................................................................12
3 Hardware Built-In-Test (BIT).............................................................................................12
4 Continuous Built-In-Test (BIT)..........................................................................................12
5 BIT Failure That Disables Ice Output ................................................................................13
6 Operator-Initiated Tests......................................................................................................14
7 Initiated Built-In-Test (BIT)...............................................................................................15
8 Correlation Counting..........................................................................................................16
9 Ice Detector RS-422 String Format....................................................................................17
10 Electrostatic Discharge (ESD) Consideration ................................................................19
APPENDIX B
1 Freezing Rain Sensor Block Diagram ................................................................................20
1.1 Microcontroller...........................................................................................................21
1.2 Watchdog/Reset Circuit..............................................................................................21
1.3 Serial EEPROM..........................................................................................................21
1.4 Probe Oscillator..........................................................................................................21
1.5 Heater Control ............................................................................................................22
1.6 Drive Coil ...................................................................................................................22
1.7 Feedback Coil.............................................................................................................22
1.8 Heater..........................................................................................................................22
1.9 DC Power Supply.......................................................................................................22
1.10 Status Output ..............................................................................................................23
1.11 Ice Signal Output........................................................................................................23
2 Qualification Capabilities...................................................................................................24
3 Input/Output Specification..................................................................................................25
3.1 Input/Output Pin Designations ...................................................................................25
1

TABLE OF FIGURES
Figure 1. MSO Circuit Schematic……………………………………………………………….5
Figure 2. MSO Circuit Sectional View………………………………………………………….5
Figure 3. Freezing Rain Sensor….………………………………………………………………6
Figure 4. Mounting………………………………...…………………………………………….7
Figure 5. Power Supply Connections…....………...…………………………………………….8
Figure 6. General Hook-up Diagram……………...……………………………………………..8
Figure 7. Functional Block Diagram……………...……………………………………………20
2

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
3

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 0.020” (0.5 mm) thickness of ice
on the probe causes the operating frequency of the probe to
decrease by approximately 130 Hz. Freezing Rain Sensor
software monitors probe frequency, and detects and annunciates
this 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 rain sensor remains in
an icing environment. The ice signal activates at 0.020” 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 0.020” 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.
4

Figure 1 MSO Circuit Schematic
Figure 2 MSO Circuit Sectional View
5

4 Physical Description
The freezing rain sensor is an integrated unit containing both the
sensor and processing electronics. It contains a 2.9” (7.35 cm)
square faceplate for mounting to the 0871LH1MNT and a 2.86”
(7.28 cm) diameter housing containing the processing electronics.
The unit weighs 0.7 lbs. (318 grams), maximum.
Figure 3 Ice Detector
5 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.
6 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.
6

7 Mounting Considerations
Figure 4 Mounting (part #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 36 inches 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 connector.
5. Secure cable to bracket with cable ties.
6. Remove shipping cover and protective cap prior to powering on
the unit.
7

8
8 Wiring Diagram - using cable Part # 0871LH1CBL-L
Datalogger Connections
Description Colour CR3000/CR1000 CR10X/CR510
Ice Blue Control Port* Control Port*
Status Yellow Control Port* Control Port*
Power Reference Black G G
Case GND Green G G
5V Power Purple 5V 5V
Shield Clear G G
*cannot share control ports
Figure 5 Power Supply Connections (part #C2155)
Figure 6 General Hook-up Diagram
Power Connections to Terminal Expander
24 VDC Red V+
24V- Black V-

9 Program Examples
9.1 CR23X
1: Timer (P26)
1: 3 Loc [ Timer ]
2: If (X<=>F) (P89)
1: 3 X Loc [ Timer ]
2: 3 >=
3: 61 F
4: 30 Then Do
3: Set Port(s) (P20)
1: 9999 C8..C5 = nc/nc/nc/nc
2: 9988 C4..C1 = nc/nc/input/input
;This Section will read the status of the ports for comparison.
;**************************************************************
4: Read Ports (P25)
1: 1 Mask (0..255)
2: 2 Loc [ IceStat ]
5: Read Ports (P25)
1: 2 Mask (0..255)
2: 1 Loc [ FaultStat ]
;Check to see if there is a fault in the unit and output it.
;***********************************************************
6: If (X<=>F) (P89)
1: 1 X Loc [ FaultStat ]
2: 1 =
3: 1 F
4: 30 Then Do
7: Do (P86)
1: 10 Set Output Flag High (Flag 0)
8: Set Active Storage Area (P80)^3085
1: 1 Final Storage Area 1
2: 10 Array ID
9: Real Time (P77)^1712
1: 1220 Year,Day,Hour/Minute (midnight = 2400)
10: Sample (P70)^23951
1: 1 Reps
2: 1 Loc [ FaultStat ]
11: End (P95)
;Check to see if there is Ice on the unit and output it.
;*******************************************************
12: If (X<=>F) (P89)
9

1: 2 X Loc [ IceStat ]
2: 1 =
3: 0F
4: 30 Then Do
13: Do (P86)
1: 10 Set Output Flag High (Flag 0)
14: Set Active Storage Area (P80)^10755
1: 1 Final Storage Area 1
2: 20 Array ID
15: Real Time (P77)^8112
1: 1220 Year,Day,Hour/Minute (midnight = 2400)
16: Sample (P70)^5446
1: 1 Reps
2: 2 Loc [ IceStat ]
;If there is ice on the unit, start a looping sequence that ends only when ice is no longer detected.
;***************************************************************************************
17: Timer (P26)
1: 0 Reset Timer
18: End (P95)
19: End (P95)
9.2 CR1000
'Declare Public Variables
Public PTemp, batt_volt
Public TimeCount
Public IceSignal
Public StatusSignal
‘ice signal: 1 = no ice, 0 = ice
‘status signal: 0 = okay, 1 = fault
'Define Data Tables
DataTable (Stat,True,-1)
Sample (1,StatusSignal,FP2)
EndTable
DataTable (Ice,True,-1)
Sample (1,IceSignal,FP2)
EndTable
DataTable (Info,1,-1)
DataInterval (0,15,Sec,10)
Minimum (1,batt_volt,FP2,0,False)
Sample (1,PTemp,FP2)
EndTable
'Main Program
BeginProg
10

11
PortsConfig (&B11,&B00)
Scan (5,Sec,0,0)
PanelTemp (PTemp,250)
Battery (Batt_volt)
TimeCount = Timer (1,Sec,0 )
If TimeCount >= 61 then
Portget (IceSignal,1 )
PortGet (StatusSignal,2)
If StatusSignal = 1 then
CallTable Stat
EndIf
If IceSignal = 0 then
CallTable Ice
Timer (1,Sec,3)
EndIf
EndIf
CallTable Info
NextScan
EndProg

Appendix A
1 RS-422 Output Format for non-Campbell Datalogger
Applications
This output operates at 9600 BAUD (One Start Bit, 8 Data Bits,
No Parity, One Stop Bit). A 24-byte string is sent once per
second. See section 10.2 for string definition.
A two-line output provides a bi-directional serial port, running at
9600 BAUD (8-bits, one Start Bit, One Stop Bit, no parity), to
allow communication with aircraft electronics and external test
equipment.
2 Built In Test (BIT)
Built-In-Test (BIT) capabilities of the freezing rain sensor consist
of hardware, continuous, power-up, and operator-initiated tests.
Whenever a failure is detected and verified, the freezing rain
sensor stops detecting and annunciating icing conditions and the
heaters are disabled. Failures detected in Initiated and Continuous
BIT are counted and enunciated once they have been verified. To
eliminate nuisance errors, failures are verified by delaying
(debouncing) the failure for a period of time. Failures detected in
Initiated BIT are latched and power must be cycled on and off to
remove a failure. If failures detected in Continuous BIT go away,
the ice detector changes back to normal mode, and once again
enables all ice detection functions.
3 Hardware Built-In-Test (BIT)
Hardware BIT is comprised of a watchdog timer that forces the
microcontroller to re-initialize if it does not receive a strobe every
1.6 seconds. An internal voltage monitor forces the
microcontroller to the reset state if the internal 5VDC power
supply falls below 4.65 VDC and holds it there until the power
supply returns above 4.65 VDC. When the microcontroller is
reset, no output string is sent.
4 Continuous Built-In-Test (BIT)
12

Continuous BIT consists of verifying the following:
•The probe heater is in the correct state. The return leg of the
heater is monitored.
•The ICE discrete output is in the correct state. The ICE discrete
output is fed back to the microcontroller through a passive
voltage divider and voltage comparator.
•The MSO is operating correctly. Frequencies between 39000 and
40150 Hz are valid.
•The probe heater is de-icing correctly. After turn-on, the probe
heater must cause the MSO frequency to return to at least 39970
Hz within the 25 second timeout or it is considered failed.
•Probe is de-iced within 25 seconds. (De-Icing Fail).
5 BIT Failure That Disables Ice Output
The Ice output is disabled due to Continuous and Initiated BIT
failures as shown in Table 1. BIT Information. Ice detection is
disabled when these failures occur because the integrity of the ice
detection capability has been compromised.
13

Table 1. BIT Information
Title Disable Ice
Detection 1Initiated
BIT Continuous BIT
MSO Fail, High X X
MSO Fail, Low X X
EEPROM Fail X
RAM Fail X X
ROM Fail X X
Watchdog Fail X
Power Interrupt Timer Fail X
Power Fault Monitor Fail X
Probe Heater Always ON or OPEN Active Test Passive Test
Probe Heater Always OFF Active Test Passive Test2
Probe Heater ON w/ 1 Enable X
De-Icing Fail Clear Only Set Only
Unknown Reset Failure X
Ice Output (not contained in 0871KB1 model) Active Test Passive Test
Note 1: When the failure is enunciated, the software no longer provides ice
detection capability.
Note 2: In Continuous BIT, the “Probe Heater Always OFF” failure is set
when the heater is ON and a de-icing failure has been detected. If the
frequency indicates that the ice has been removed within the expected time,
the software will not annunciate the probe heater failure. The actual failure is
most likely due to a problem in the heater feedback circuitry rather than heater
control circuitry. The failure will be enunciated the next time IBIT is
performed.
6 Operator-Initiated Tests
The operator can test the freezing rain sensor functionality by
squeezing the tip of the probe between the index finger and
thumb. This simulates icing by decreasing the frequency of the
probe.
With the sensor wired to the datalogger use a digital voltmeter
(DVM); measure DC voltage signal between the Ice signal (blue
wire in control port) and the power reference ground (black wire
in G terminal). The voltage reading should be 4500mvDC to
5000mvDC. When the probe tip of the ice detector is squeezed;
14

thus changing the frequency and tripping the probe, the voltage
reading will immediately drop to a reading below 500mvDC.
Observing this will verify that the probe is operating properly and
give the user enough time to release the probe before it reaches
its full heating temperature.
Caution: Once initiated, the heating (de-icing) sequence will
quickly heat the probe to 204.4°C. Though bare fingers must
be used for a reliable test result, there is a danger that you
will burn your fingers if you do not let go when heating has
been verified.
7 Initiated Built-In-Test (BIT)
Initiated BIT is performed at initial power-up of the freezing rain
sensor and following power interruptions of not less than 200 ms.
Initiated BIT consists of the following tests:
•The ice and fault status outputs are set in the RS-422 string and
on the discrete outputs so monitoring electronics or test
equipment can verify activation.
•The freezing rain sensor heater is turned on for a short period of
time to verify correct operation of the heater, heater control
circuit, and heater feedback circuit.
•Correct operation of the watchdog timer is verified by simulating
a microcontroller time-out and waiting for a reset input.
•Proper ROM operation is verified by computing a checksum of
the ROM contents and comparing against a a checksum stored in
the ROM.
•RAM operation is verified by writing and reading test bytes.
•The Power Interrupt Timer is checked by verifying its transitions
to a “warm” state after performing a “cold” start.
•The power fail input is pulled down to verify a power failure is
detected.
•Each time the critical data from the Serial EEPROM is read, a
checksum is read and compared to the checksum computed from
the contents. Each time critical data is written to the Serial
EEPROM, a checksum is computed and stored with the data.
15

16
•Resets due to unknown reasons (such as reset from the watchdog
timer) are detected.
Initiated BIT will examine the RESET EEPROM input. If the
input is active, the STATUS output will be set to FAIL and the
ICE output and probe heater will be disabled. (This feature
allows a factory technician to perform the MSO capacitor
selection process without activation of the probe heater.)
Activation of the Press-to-Test (PTT) input for greater than 100
ms also causes the ice detector to perform Initiated BIT. The PTT
input is ignored when the ice output is actibe. After PTT is
completed, the correlation count is restored to its pre-test value.
Initiated BIT is complete within 3 ± seconds of initial power up.
8 Correlation Counting
The freezing rain sensor tracks the amount of ice accumulation
on the probe during an icing enoucnter. The correlation count is a
value tracked by the freezing rain sensor that indicates the
amount of ice that has accumulated on the probe during the icing
encounter. Each correlation count equals 0.010 inches of ice.
The correlation count, ranging from 0 to 255, indicates the
number of times the MSO frequency decreases by 65 Hz during
an icing encounter. A decrease in frequency of 65 Hz correlates
to an equivalent 0.25 mm of ice that would have formed on the
ice detector probe, neglecting the change in collection efficiency
caused by ice build-up. Upon reaching a correlation count of 255,
the value is no longer incremented.
The freezing rain sensor compensates by adding a value (ranging
from 0 to 6) to the correlation count when the ice detection cycle
is completed, to account for the ice that would have accumulated
if the heater had not been on.
The correlation count is in the serial string, Table 3. Serial String
Format.
The correlation count is initialized to zero at unit power up.

9 Ice Detector RS-422 String Format
Table 3. Serial String Format
Byte Bit Definition Comments/Interpretation/Range
0 (First) 7 (MSB) String ID Presently defined as 00
6 May add additional strings in future
5 - 3 Unused
2 Probe Heater State 1- Heater On
0- Heater Off
1 Ice Output 1- Ice
0- No Ice
0 Status Output 1- Fail
0- (OK) No Fail
1 -2 MSO FREQUENCY MSO Count in Hex Frequency = 774060000/Dec (MSO)
3 - ERRSTAT1 7 Unused 1 = Active
6 MSA Fail, Too High
5 MSO Fail, Too Low
4 EEPROM Fail
3 RAM Fail
2 ROM Fail
1 Watchdog Fail
0 Power Interrupt Timer Fail
4 - ERRSTAT2 7 - 6 Probe Heater Failure 00 = Probe Heater OK
01 = Probe Heater Always ON or OPEN
10 = Probe Heater Always OFF
11 = Probe Heater ON with 1 Enable
5 De-Icing Fail 1 = Active
4 Unused
3 Unused
2 Unused
1 Unused
0 Unused
17

18
Table 3. Serial String Format continued
5 - 7 ON-TIME CNT Power-On Time (In Hex) in 10-Minute Increments 00 - 01FFFF
8 - 9 COLD START CNT Cold Start Power-On Count 00 - FFFF
10-11 ICE CNT Ice Events 00 - FFFF
12 - FAIL CNT Total Failures Encountered. This number is incremented
each time the ice detector transitions from OK to fail. 00 - FF
13 - FAIL DTL 1 7 - 4 MSO Frequency Fail Count 0 - F
3 - 0 Heater Fail Count 0 - F
14 - FAIL DTL 2 7 - 4 Not Used Not Used
3 - 0 Not Used Not Used
15 - LAST ERR 1 See ERRSTAT1 Above
16 - LAST ERR 2 See ERRSTAT2 Above
17 - 2ND LAST ERR 1 See ERRSTAT1 Above
18 - 2ND LAST ERR 2 See ERRSTAT2 Above
19 - PERM ERR 1 See ERRSTAT1 Above
20 - PERM ERR 2 See ERRSTAT2 Above
21 - Software Version 7 - 0 Software Version per VDD/SC1 0 - FF
22 - Correlation Count 7-0 0.01" ice accretion increments since power-on 0 - FF
23 - CHECKSUM Summation (1-byte wide) of bytes 0 - 22 0 - FF