Campbell Scientific 0871LH1 User Manual

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

9.1

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-

Figure 5 General Hook-up Diagram

9.2

0871LH1CBL -L W ir in g fo r RS 42 2 Ou tp ut

9

NOTE:

NOTE:

Description Pin Colour Sensor – MD485

Power Reference B Black N/C G

Case GND C Green N/C G

5V Power Purple N/C G

The MD485 Multidrop Interface, the L15966 Wall Charger and the SC110
Interface Cable are required to measure the RS422 output on a CR1000 or
CR3000.

The MD485 Multidrop Interface must be configured for Active Ports |
RS232 and RS485, RS232 Baud Rate | 9600, and RS485 Baud Rate | 9600.
Refer to the MD485 Manual for configuration instructions.

Table 4. Datalogger Connections

Sensor –

CR1000/CR3000

Ice F Blue N/C N/C

Status G Yellow N/C N/C

RS422 A D White RS485 A N/C

RS422 B E Brown RS485 B N/C

Shield Clear N/C G

8

10.1

CR1000 Examp le – D is cr et e Ou tp ut s

NOTE:

If the application requires the monitoring of the discrete outputs the 5Vdc
connection must be made.

WARNING:

Isolate wires that are not connected as they may cause problems if
shorted to ground.

DB9 Male Connector

10 Program Examples

It is possible to collect icing information either by the discrete outputs of
the 0871LH1, or the available RS422 output.

Table 5. Power Connections to Terminal Expander

Description Pin Colour Connection

24VDC A Red V+

24VDC Return B Black V-

Table 6. SC110 Connections

Description

CR1000 Tx

CR1000 Rx

CR1000 Gnd

Shield

Colour MD485 CR1000/CR3000

RS-232 (to DTE) N/C

Brown N/C C3

White N/C C4

Yellow N/C G

Clear N/C G

1

'Declare Public Variables

Public TimeCount
Public IceSignal 'ice signal: Open = no ice, Ground = ice
Public StatusSignal 'status signal: Ground = okay, Open = fault

'Define Data Tables

DataTable (Sensor_Status,True,-1)
Sample (1,StatusSignal,FP2)
EndTable

DataTable (Ice_Condition,True,-1)
Sample (1,IceSignal,FP2)
EndTable

'Main Program
BeginProg

'In order for the datalogger to receive data from the 0871LH1, 'ports 1 & 2 must be configured as inputs.
PortsConfig (&B11,&B00)

9

Monitor the discrete outputs of the 0871LH1 for icing events and changes
to the sensor status. Data tables are updated only after an icing event or
status change occurs.

Scan (5,Sec,0,0)

10.2

CR23X Exam pl e – Di sc re te O ut pu ts

'Start timer to corrdinate monitoring of ice signal output from sensor
TimeCount = Timer (1,Sec,0 )

'During icing event the sensor cycles through a 60 second monitoring 'interval. When the first icing event occurs

'a 60 second counter is started in the sensor. Once the 60 seconds have pasted the sensor will determine

'if further icing has occurred. If yes, the sensor signals the icing event, heats the probe, and resets counter.

'If no, the sensor signals no ice and resets counter.
If TimeCount >= 61 Then

'Record sensor outputs for icing and status. Based on scan rate.
PortGet (IceSignal,1 )
PortGet (StatusSignal,2)

'If a status fault is detected then the status code is stored to the Sensor Status data table.

'Only fault status data is stored to the table.
If StatusSignal = 1 Then
CallTable Sensor_Status
EndIf

'If an icing event is detected then store the record to the Ice Condition data table.

If IceSignal = 0 Then
CallTable Ice_Condition

'Reset the datalogger counter during icing events so that data is'coordinated with the sensors counter.

Timer (1,Sec,3)
EndIf
EndIf
NextScan
EndProg

1

;Set Timer input location

1: Timer (P26)
1: 3 Loc [ Timer ]

;Use Timer to monitor Control Ports 1 & 2 every 61 seconds

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

;Read the status of the ports and store to input locations 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 sensor and output it to final storage.

6: If (X<=>F) (P89)
1: 1 X Loc [ FaultStat ]
2: 1 =
3: 1 F

10

4: 30 Then Do

10.3

CR1000 Exa mp le – R S4 22 O ut pu ts

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 sensor and output it to final storage.
12: If (X<=>F) (P89)
1: 2 X Loc [ IceStat ]
2: 1 =
3: 0 F
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)

1

NOTE:

The MD485 Multidrop Interface, the L15966 Wall Charger and the SC110
Interface Cable are required to measure the RS422 output on a CR1000 or
CR3000.

NOTE:

The MD485 Multidrop Interface must be configured for Active Ports |
RS232 and RS485, RS232 Baud Rate | 9600, and RS485 Baud Rate | 9600.
Refer to the MD485 Manual for configuration instructions.

11

'CR1000 Series Datalogger

'Declare Public Variables

Public PTemp, batt_volt
Public LH1_Byte_Count As Float
Public Read_LH1 As Boolean
Public Ice
Public Ice_mm

'Define the Comport for the 0871LH1 here:

Const LH1_comport = Com2

'*******************************************************************************************
'Public Variables from 0871LH1 Sensor via RS-422 Output
'*******************************************************************************************

Public LH1_Serial_Error As Boolean

'This is the decimal equivalent of Bytes 1 to 24 output by the 0871LH1

Public LH1_Byte(24) As Long

'String is 1 - On or 0 - Off

Public LH1_Probe_Heater_State As String * 3

'String is 1 - Ice or 0 - No Ice

Public LH1_Ice_Output As String * 6

'String is 1 - Fail 0 - OK

Public LH1_Status_Output As String * 4

'String is 1 - Fail 0 - OK
'ERRSTAT1

Public LH1_ERR_MSO_TOO_HIGH As String * 4
Public LH1_ERR_MSO_TOO_LOW As String * 4
Public LH1_ERR_EEPROM As String * 4
Public LH1_ERR_RAM As String * 4
Public LH1_ERR_ROM As String * 4
Public LH1_ERR_WATCHDOG As String * 4
Public LH1_ERR_PWR_INT_TIMER As String * 4

'ERRSTAT2

Public LH1_ERR_DE_ICING As String * 4

'00 - OK, 01 - Always On. 10 - Always Off, 11 - ON

Public LH1_ERR_PROBE_HEATER As String * 10

Public LH1_MSO_Frequency As Float
Public LH1_ON_Time_Days As Float
Public LH1_Cold_Start_Count As Float
Public LH1_ICE_Count As Float
Public LH1_FAIL_Count As Float
Public LH1_MSO_FAIL_Count As Float
Public LH1_Heater_FAIL_Count As Float
Public LH1_Software_Version As Float
Public LH1_ICE_Count_From_PWR_ON As Float
Public LH1_CHECKSUM As Long

'*******************************************************************************************
'END - Public Variables for 0871LH1 RS-422 Output
'*******************************************************************************************

'Define Data Tables
'PLEASE NOTE: The majority of 0871LH1 outputs are diagnostic in nature. Add to Data Table(s)
' as required for your application.

DataTable (LH1_output,1,1000)

12

DataInterval (0,15,Sec,10)
Minimum (1,batt_volt,FP2,0,False)
Sample (1,PTemp,FP2)
Sample (1,Ice,IEEE4)
Sample (1,Ice_mm,IEEE4)
EndTable

'This Subroutine Sets all values to a Defaut Error State if Serial Communications do not work

Sub LH1_Error_State
LH1_Probe_Heater_State = "NAN"
LH1_Ice_Output = "NAN"
LH1_Status_Output = "NAN"
LH1_ERR_MSO_TOO_HIGH = "NAN"
LH1_ERR_MSO_TOO_LOW = "NAN"
LH1_ERR_EEPROM = "NAN"
LH1_ERR_RAM = "NAN"
LH1_ERR_ROM = "NAN"
LH1_ERR_WATCHDOG = "NAN"
LH1_ERR_PWR_INT_TIMER = "NAN"
LH1_ERR_DE_ICING = "NAN"
LH1_ERR_PROBE_HEATER = "NAN"

LH1_MSO_Frequency = NAN
LH1_ON_Time_Days = NAN
LH1_Cold_Start_Count = NAN
LH1_ICE_Count = NAN
LH1_FAIL_Count = NAN
LH1_MSO_FAIL_Count = NAN
LH1_Heater_FAIL_Count = NAN
LH1_Software_Version = NAN
LH1_ICE_Count_From_PWR_ON = NAN
LH1_CHECKSUM = NAN
EndSub

'******************************************************************************************
'0871LH1_GetData Subroutine (Typically Takes 3 Seconds to execute)
'******************************************************************************************
'Use an MD485 configured to RS-485, RS-232 Transparent Mode. 9600 BAUD for RS-232 and RS-485

Sub LH1_GetData
Dim Stay_In_Loop As Boolean
Dim CheckForBlankTime As Boolean
Dim LoopCounter
Dim Old_Byte_Count As Float
Dim TimeSinceLastByte As Float
Dim LH1_Raw_In_Buff As String * 50

SerialFlush (LH1_comport)

'Obtain the current byte count

Old_Byte_Count = SerialInChk (LH1_comport)

'Initializations reset and start the timer
Timer (1,mSec,2)
CheckForBlankTime = False
LH1_Serial_Error = False
Stay_In_Loop = True

While Stay_In_Loop = True
'Get the existing byte count
LH1_Byte_Count = SerialInChk (LH1_comport)

'reset the timer if the byte cound is not the same

If LH1_Byte_Count <> Old_Byte_Count Then

13

'update the byte count
Old_Byte_Count = LH1_Byte_Count

'reset and start the timer

Timer (1,mSec,2)

'Received at least one byte start checking for a blank time
CheckForBlankTime = True
EndIf

'Obtain the time from the last byte.

TimeSinceLastByte = Timer (1,mSec,4)

If CheckForBlankTime = True Then

'If no characters occur within 100 msec of last byte then assume end of packet.

If TimeSinceLastByte > 100 Then Stay_In_Loop = False
EndIf

'Exit regardless if more than 3 seconds elapse

If TimeSinceLastByte > 3000 Then
LH1_Serial_Error = True
Stay_In_Loop = False
EndIf

Wend

If LH1_Serial_Error = False Then
'Flush the buffer
SerialFlush (LH1_comport)

'Wait a mximum of 2 seconds

If Timer (2,mSec,4) > 2000 Then
LH1_Serial_Error = TRUE
Stay_In_Loop = False
EndIf

Wend

'Obtain a CheckSum and convert All Binary Values
LH1_CHECKSUM = 0
'Convert all the BINARY Values
For LoopCounter=1 To 24 Step 1
LH1_Byte(LoopCounter) = ASCII (LH1_Raw_In_Buff(1,1,LoopCounter))

If LoopCounter <> 24
LH1_CHECKSUM = LH1_CHECKSUM + LH1_Byte(LoopCounter)
EndIf
Next
LH1_CHECKSUM = LH1_CHECKSUM AND &B11111111
If LH1_CHECKSUM <> LH1_Byte(LoopCounter) Then LH1_Serial_Error = TRUE
EndIf

If LH1_Serial_Error = TRUE Then
Call LH1_Error_State
Else
'For LH1 Byte 1
'BIT 0 - Status Output
If (LH1_Byte(1) AND &B00000001) <> 0 Then
LH1_Status_Output = "Fail"
Else
LH1_Status_Output = "OK"
EndIf

14

'BIT 1 - Ice Output
If (LH1_Byte(1) AND &B00000010) <> 0 Then
LH1_Ice_Output = "Ice"
Else
LH1_Ice_Output = "No Ice"
EndIf

'BIT 2 - Probe Heater State
If (LH1_Byte(1) AND &B00000100) <> 0 Then
LH1_Probe_Heater_State = "On"
Else
LH1_Probe_Heater_State = "Off"
EndIf

'0871LH1 Bytes 2 and 3 are MSO Frequency count
'Calculate Frequency from the count as follows
LH1_MSO_Frequency = 774060000/((LH1_Byte(2) << 8) + LH1_Byte(3))

'Byte 4 is the ERRSTAT1

If (LH1_Byte(4) AND &B1) <> 0 Then
LH1_ERR_PWR_INT_TIMER = "FAIL"
Else
LH1_ERR_PWR_INT_TIMER = "OK"
EndIf

If (LH1_Byte(4) AND &B10) <> 0 Then
LH1_ERR_WATCHDOG = "FAIL"
Else
LH1_ERR_WATCHDOG = "OK"
EndIf

If (LH1_Byte(4) AND &B100) <> 0 Then
LH1_ERR_ROM = "FAIL"
Else
LH1_ERR_ROM = "OK"
EndIf

If (LH1_Byte(4) AND &B1000) <> 0 Then
LH1_ERR_RAM = "FAIL"
Else
LH1_ERR_RAM = "OK"
EndIf

If (LH1_Byte(4) AND &B10000) <> 0 Then
LH1_ERR_EEPROM = "FAIL"
Else
LH1_ERR_EEPROM = "OK"
EndIf

If (LH1_Byte(4) AND &B100000) <> 0 Then
LH1_ERR_MSO_TOO_LOW = "FAIL"
Else
LH1_ERR_MSO_TOO_LOW = "OK"
EndIf

If (LH1_Byte(4) AND &B1000000) <> 0 Then
LH1_ERR_MSO_TOO_HIGH = "FAIL"
Else
LH1_ERR_MSO_TOO_HIGH = "OK"
EndIf

If (LH1_Byte(5) AND &B011000000) = &B00000000 Then
LH1_ERR_PROBE_HEATER = "OK"

15

ElseIf (LH1_Byte(5) AND &B011000000) = &B01000000 Then
LH1_ERR_PROBE_HEATER = "Always On"
ElseIf (LH1_Byte(5) AND &B011000000) = &B10000000 Then
LH1_ERR_PROBE_HEATER = "Always Off"
ElseIf (LH1_Byte(5) AND &B011000000) = &B11000000 Then
LH1_ERR_PROBE_HEATER = "On"
EndIf

If (LH1_Byte(5) AND &B001000000) <> 0 Then
LH1_ERR_DE_ICING = "FAIL"
Else
LH1_ERR_DE_ICING = "OK"
EndIf

'0871LH1 output ON time in 10 Minute Increments
LH1_ON_Time_Days = ((LH1_Byte(6) << 16) + (LH1_Byte(7) << 8) +LH1_Byte(8))/144
LH1_Cold_Start_Count = (LH1_Byte(9) << 8) +LH1_Byte(10)
LH1_ICE_Count = (LH1_Byte(11) << 8) +LH1_Byte(12)
LH1_FAIL_Count = LH1_Byte(13)
LH1_MSO_FAIL_Count = LH1_Byte(14)>>4
LH1_Heater_FAIL_Count = LH1_Byte(14) AND &B00001111
LH1_Software_Version = LH1_Byte(22)
LH1_ICE_Count_From_PWR_ON = LH1_Byte(23)

EndIf
EndSub

'Main Program
BeginProg

'Ensure that the proper Com port is defined for the Constant LH1_comport
SerialOpen (LH1_comport,9600,3,0,50)

Scan (15,Sec,0,0)
PanelTemp (PTemp,250)
Battery (batt_volt)
'Enter other measurement instructions

'Inteval Time for Reading the Ice Detector
If TimeIntoInterval(0,1,Min) Then Read_LH1 = True
Read_LH1 = True

If Read_LH1 = True Then
Call LH1_GetData
Read_LH1 = False
EndIf

'++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
'NOTE: The use of the Ice thickness calculation is discretionary and dependant on the
' application. The maximum allowable ice is 0.02" before the heater turns on.

'Formula used to convert the Frequency into Ice Thickness (inches).
Ice = -0.00015*LH1_MSO_Frequency + 6
'Convert ice accumulation from inches to millimeters
Ice_mm = Ice * 25.4
'++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

CallTable LH1_output
NextScan
EndProg

16

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 9,
Table 3 for string definitions.

A two-line output provides a unidirectional 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)

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.

17

• 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.

Table 7. BIT Information

Title

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

NOTE:

When the failure is enunciated, the software no longer provides
ice detection capability.

Disable Ice

Detection

Initiated BIT

1

Continuous

BIT

NOTE:

18

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; 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.

• 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

19

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 encounter. 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 0.25mm (0.01”) 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 0.25mm 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.

20

1- Heater On

0- Heater Off

1- Ice

0- No Ice

Table 8. Serial String Format

String ID Presently defined as 00

May add additional strings in future

Probe Heater State

Ice Output

Byte Bit Definition Comments/Interpretation/Range

1 = Active

00 = Probe Heater OK

01 = Probe Heater Always ON or OPEN

10 = Probe Heater Always OFF

Probe Heater Failure

1 = Active

11 = Probe Heater ON with 1 Enable

0 (First) 7 (MSB)

6

5 - 3 Unused

2

1

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

6 MSA Fail, Too High 5 MSO Fail, Too Low 4 EEPROM Fail

9 Ice Detector RS-422 String Format

3 RAM Fail 2 ROM Fail 1 Watchdog Fail

0 Power Interrupt Timer Fail 4 - ERRSTAT2 7 - 6

5 De-Icing Fail

4 Unused

3 Unused

2 Unused

1 Unused

0 Unused

00 - FF

time the ice detector transitions from OK to fail.

Table 8. 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

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

The freezing rain sensor internal components are ESD sensitive, class 1, so proper ESD precautions must be observed

(wrist straps, conductive surfaces) when handling.

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

10 Electrostatic Discharge (ESD) Consideration

22

Appendix B

d

1 Freezing Rain Sensor Block Diagram

The block diagram in Figure 4: Functional Block Diagram provi
understanding of the functionality of the freezing rain sensor.

Figure 6 Functional Block Diagram

23

1

1.1

Microcontroller

1.2

Watchdog/R es et C ircu it

1.3

Serial EEPROM

1.4

Probe Oscillator

1.5

Heater Control

The freezing rain sensor uses an Intel 87C51-type microcontroller to
control the freezing rain sensor functions. This 8-bit microcontroller
requires at least: 4 Kbytes of on-board ROM, 128 bytes of RAM, and 32
input/output ports. The freezing rain sensor uses about 75% of these
resources. Upgraded microcontrollers that provide more resources are
available. The microcontroller runs at 7.372 MHz.

The watchdog timer/reset circuit monitors the microcontroller and
provides a reset pulse if not periodically toggled. The watchdog also
provides reset pulses on initial power-up and holds the microcontroller in
the reset state if the internal power supply falls below an acceptable
voltage. The watchdog indicates impending power loss so the ice
detector can shut down in a known manner.

The Serial EEPROM stores unit status (icing state, failure state, heater
state, correlation count) which is recovered after power interruptions of
200 ms or less. This allows the unit to meet the power interruption
requirements of RTCA DC-160C, Section 16, Category Z. Additionally, the
Serial EEPROM stores environmental and failure information such as unit
elapsed-time, number of icing encounters, number of failures, and
detailed information on types and quantities of each annunciated failure.
This information is used by Rosemount Aerospace to confirm and repair
failures reported by the end user and also to collect MTBF data. Each time
the Serial EEPROM is written, a checksum is computed and written. Each
time the Serial EEPROM is read, a checksum is computed and compared
to the stored value.

The probe oscillator is the electronic control portion of the
magnetostrictive oscillator (MSO) used to sense and detect ice. This
circuit provides the drive and feedback of the ice sensing probe. The
circuit drives the probe at a nominal 40kHz, and converts the feedback
into a CMOS compatible square wave that is measured by the
microcontroller. As ice accretes on the probe, the frequency decreases,
and it is this frequency change that the microcontroller annunciates in
the form of Ice Signal #1.

The heater control turns the probe heater on and off as commanded by
the microcontroller and monitors the actual heater state (ON or OFF) for
verification by the microcontroller. Two outputs are required from the
microcontroller to turn on the heater. This minimizes the possibility of an
unintended heater ON condition. The heater control also monitors the
state of the heater and provides feedback to the microcontroller so that it
can be determined whether the heater is on or off.

24

1

1.6

Drive Coil

1.7

Feedback Coil

1.8

Heater

1.9

DC Power Supply

1.10

Status Output

1.11

Ice Signal Output

The drive coil modulates the magnetic field of the magnetostrictive
oscillator and causes an ultrasonic axial movement of the probe.

The feedback coil senses the movement of the probe and when
employed in the probe oscillator circuit, completes the feedback portion
of the MSO.

The probe heater de-ices the probe. It is activated when the nominal

icing trip point of 0.50mm is reached and is turned off five seconds after

the MSO has returned to at least 39,970 Hz (the additional five seconds

allows the strut probe time to shed the de-bonded ice). The maximum

heater ON time is 25 seconds. If the probe frequency has not returned at

least 39,970 Hz by that time, a de-ice failure is declared and the heaters

are turned off. An open circuit of the heater is detected by the

microcontroller.

The DC power supply provides 24 VDC for the heater circuitry. Internal
circuitry converts the 24 VDC input power to 5 VDC for use by the
microcontroller and associated circuits. It employs a large input capacitor
to provide enough time between detection of input power loss and
actual loss of DC power, for the microcontroller to store the current unity
status in the non-volatile memory. The DC power supply provides input
transient protection to meet RTCA DO-160C power input, voltage spike,
and lightning requirements.

The status output provides a ground output when the freezing rain
sensor is operating correctly, and high impedance (200 KΩ minimum)

when the unit has detected a failure. Failures are detected through
continuous and initiated tests. The Status output is capable of sinking 50
mA and is guaranteed to be no more than 1.5 VDC with respect to Signal
Return when active. This output is transient protected to meet RTCA DO­160C lightning requirements and to prevent stray high-voltage from
coupling into the unit and damaging the output transistor.

The Ice Signal output provides a ground output for 60 ± 6 seconds when
the ice detector has detected the presence of ice (frequency drop of 130
Hz, equivalent to approximately 0.50mm ice formation). If the frequency
subsequently decreases by 130 Hz while the Ice Signal output timer is
non-zero, the timer is reinitialized to 60 seconds.

The output is transient protected to meet RTCA DO-160C lightning
requirements and to prevent stray high-voltage from coupling into the
unit and damaging the output transistor.

The ice output has feedback to the microcontroller for software to verify
it is in the correct state for more built in test coverage. The software in the

25

0871LH1 model uses this feedback to verify that the ice output is
operating correctly.

To interface to the 0871LH1, the power supply must provide a pull-up of

5.3 volts maximum. When the ice output is inactive (open), the nominal
resistance to ground is 10.1 KΩ. The power supply should source at least

0.250 mA to provide the proper signal to the Ice Signal feedback circuitry.
When the output is active (closed), it is capable of sinking 50 mA and is
guaranteed to be no more than 1.5 VDC with respect to Signal Return.

2 Qualification Capabilities

Table 9. 0871LH1 Ice Detector Qualification Capabilities

Test Name Test Requirement

EMC

Lightning Induced
Susceptibility

Temperature Variation DO-160C: Cat A
Temperature/Altitude DO-160C: Cat D2 (-55°C to +71°C)
Vibration DO-160C: Cat E (Random, 7.9 grms)
Operation Shock, Crash Safety DO-160C: Shock
Salt Spray DO-160C: Cat S
Humidity DO-160C: Cat B
Icing Performance Rosemount Aerospace, Inc. Test Procedure
Power Input DO-160C: Cat Z, 18 - 29.5 VDC
Voltage Spike DO-160C: Cat A
Magnetic Effect DO-160C: Cat A (1 deflection at 0.5m)

Bonding

Dielectric Withstanding MIL-STD 202, 500 VAC, 60 Hz, EMI Filters Disconnected
Insulation Resistance MIL-STD 202, 500 VDC, 1000 MW, EMI Filters Disconnected
Fluid Susceptibility DO-160C: Cat F
Waterproofness DO-160C: Cat W
Fungus Resistance DO-160C: Cat F
Sand and Dust DO-160C: Cat D
Direct Lightning Strike DO-160C: Cat 1A
Software DO-178B used as a guideline

DO-160C:
Audio Freq Susc: Cat Z
Induced Signal: Cat Z
Susc: Chg Notice 3, Cat R
RF Susceptibility: Cat Z
RF Emissions: Cat Z
DO-160C:
Multiple Burst: Waveform 3 & 4: Level 3
Multiple Stroke: Waveform 3: Level 3

2.5 mW Max. Mounting Plate to Aircraft Structure
10 mW Max. Connector Shell to Mounting Plate

26

3 Input/Output Specification

3.1

Input/Outp ut P in D esigna ti on s

3

Table 10. Input/Output Pin Designations

Signal Name

24VDC A Input 18-29.5 VDC**

24VDC Return B Input ---- ---- 20

Case Ground C Input ---- ---- 20

RS-422 High D Output Per RS-422 Spec Per RS-422 Spec 20-24

RS-422 Low E Output Per RS-422 Spec Per RS-422 Spec 20-24

Ice F Output Ground Active (1.5V Max) 0.5 - 50 mA 20-24

Open Inactive

Status G Output Ground Inactive (1.5V Max) 0.5 - 50 mA 20-24

Open Active

**Ice will be correctly detected between these voltages. Proper probe de-icing, however, is only
guaranteed when input voltage is 24VDC or greater.

Connector

Pin

Input or

Output

Definition Current

1.5 Amp Max at
28VDC

Wire

Gauge

20

27

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