Campbell 0871LH1 Instruction Manual

INSTRUCTION MANUAL

0871LH1

Freezing Rain Sensor

December 2008

Copyright © 2007

Campbell Scientific (Canada)Corp.

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

2

General

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.

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 60­second 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.

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.

Power Interruptions

6

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.

Figure 3 Ice Detector

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 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

Power Connections to Terminal Expander

24 VDC Red V+

24V- Black V-

*cannot share control ports

Figure 5 Power Supply Connections (part #C2155)

Figure 6 General Hook-up Diagram

8

9 Program Examples

CR23X

9.1

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: 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)

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

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

11

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.

Hardware Built-In-Test (BIT)

3

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
MSO Fail, High
MSO Fail, Low
EEPROM Fail
RAM Fail
ROM Fail
Watchdog Fail
Power Interrupt Timer Fail
Power Fault Monitor Fail
Probe Heater Always ON or OPEN
Probe Heater Always OFF
Probe Heater ON w/ 1 Enable
De-Icing Fail
Unknown Reset Failure
Ice Output (not contained in 0871KB1 model)

Disable Ice
Detection

X X
X X

X
X X
X X

X

X

X

Active Test Passive Test

Active Test Passive Test

X

Clear Only Set Only

X

Active Test Passive Test

1

Initiated

BIT

Continuous

BIT

2

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

• 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.

16

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

10 Electrostatic Discharge (ESD) Consideration

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

Appendix B

1 Freezing Rain Sensor Block Diagram

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

Figure 7 Functional Block Diagram

20

1.1 Microcontroller

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.

1.2 Watchdog/Reset Circuit

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.

1.3 Serial EEPROM

Probe Oscillator

1.4

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,

21

1.5 Heater Control

Drive Coil

1.6

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.

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

1.7 Feedback Coil

1.8 Heater

1.9 DC Power Supply

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 0.020” 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

22

1.10 Status Output

1.11 Ice Signal Output

microcontroller to store the current unity status in the non­volatile 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 DO-160C 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 0.020”
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 0871KB2 model uses this feedback to verify that
the ice output is operating correctly. However, in the 0871KB1
model, the software does not use this input.

To interface to the 0871 KB, the power supply must provide a
pull-up to 5 to 28 volts. When the ice output is inactive (open),
the nominal resistance to ground is 13.4 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.

23

2 Qualification Capabilities

0871KB Ice Detector Qualification Capabilities

Test Name Test Requirement

EMC

Lightning Induced Susceptibility

Temperature Variation DO-160C: Cat A
Temperature/Altitude DO-160C: Cat D2 (-40°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

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 mΩ Max. Mounting Plate to Aircraft Structure
10 mΩ Max. Connector Shell to Mounting Plate

MIL-STD 202, 500 VDC, 1000 MΩ, EMI Filters
Disconnected

24

3 Input/Output Specification

3.1 Input/Output Pin Designations

Table 2. Input/Output Pin Designations

Signal Name Con-

nector

Pin

24VDC A

Input or
Output

Input 18-29.5 VDC**

Definition Current Wire

Gauge

1.5 Amp Max at
28VDC 20

24VDC Return B
Case Ground C

RS-422 High D
RS-422 Low E
Ice F

Status G

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

Input ---- ---- 20

Input ---- ---- 20
Output Per RS-422 Spec Per RS-422 Spec 20-24
Output Per RS-422 Spec Per RS-422 Spec 20-24
Output Ground Active (1.5 VDC Max) 0.5 - 50 mA 20-24

Open Inactive

Output Ground Active (1.5 VDC Max) 0.5 - 50 mA 20-24

Open Inactive

25