Campbell Scientific 0871LP1 Instruction Manual

INSTRUCTION MANUAL

0871LP1

Freezing Rain Sensor

July 2020

Campbell Scientific (Canada)Corp.

Table of Contents

Section 1. Purpose ..................................................................................................................................... 3

Section 2. General ...................................................................................................................................... 3

Section 3. Detailed Principle of Operation ................................................................................................ 3

Section 4. Physical Description ................................................................................................................. 5

Section 5. Temperature Considerations ..................................................................................................... 6

Section 6. Power Interruptions .................................................................................................................. 6

6.1 Disconnection from Supply Source ............................................................................................ 6

6.2 Protection Against Electric Shock – External Circuit Connections ................................................ 6

Section 7. Mounting Considerations .......................................................................................................... 7

Section 8. Wiring Diagram - using cable Part # 0871LP1CBL-L ............................................................. 7

Table 1. Datalogger Connections ...................................................................................................... 7

Table 2. Power Connections to C2673 (24VDC Power Supply)....................................................... 8

Section 9. Program Example ..................................................................................................................... 9

9.1 CR1000X .................................................................................................................................... 9

Section 10. RS-485 Output Format for non-Campbell Datalogger Applications ............................ 16

10.1 Valid Request Codes .................................................................................................................... 16

Table 3. Valid Request Codes ......................................................................................................... 16

Section 11. Built-In-Test (BIT) ............................................................................................................... 17

11.1 Hardware Built-In-Test (BIT) ...................................................................................................... 17

11.2 Continuous Built-In-Test (BIT) ................................................................................................... 17

11.3 BIT Failure That Disables Ice Output ................................................................................... 18

Table 4. BIT Information ................................................................................................................. 18

11.4 Operator-Initiated Tests ......................................................................................................... 19

11.5 Initiated Built-In-Test (BIT) .................................................................................................. 19

Section 12. Correlation Counting ............................................................................................................ 20

Section 13. Electrostatic Discharge (ESD) Consideration ...................................................................... 20

Section 14. Ice Detector RS-485 String Format ...................................................................................... 21

Table 5. Serial String Format ........................................................................................................... 21

Section 15. Functionality Descriptions .................................................................................................... 23

15.1 Microcontroller ............................................................................................................................ 23

15.2 Watchdog/Reset Circuit ............................................................................................................... 23

15.3 Serial EEPROM ........................................................................................................................... 23

15.4 Probe Oscillator ........................................................................................................................... 23

15.5 Heater and Heater Control ........................................................................................................... 24

15.6 Drive and Feedback Coil ............................................................................................................. 24

15.7 DC Power Supply ........................................................................................................................ 24

15.8 Status Output ............................................................................................................................... 25

15.9 Ice Signal Output ......................................................................................................................... 25

Appendix A Freezing Rain Sensor Block Diagram ................................................................................. 26

Appendix B. Input/Output Pin Designations ........................................................................................... 27

Table 6. Input/Output Pin Designations .......................................................................................... 27

Appendix C Qualification Capabilities .................................................................................................... 28

Table 7. Qualification Capability Levels ......................................................................................... 28

Section 1. Purpose

This document provides detailed information about the Collins Aerospace model 0871LP1 Freezing Rain Sensor for use in ground-based meteorological applications. Topics covered include requirements, qualification categories and methodology, and detailed design information.

Section 2. General

The Collins Aerospace 0871LP1 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-485 interface (RS-232 is available with a line level converter) and one discrete output which is the Status Output. The discrete Ice signal output is essentially non-functional in this model 0871LP1, and no external connection is required.

One freezing rain sensor is used on each station and provides the primary means of ice detection or an icing condition so that appropriate actions can be taken.

Section 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 0.020” (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.

Note: by default, the heater power is not automatic and is controlled in the programming of the sensor.

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 if the freezing rain sensor remains in an icing environment. The ice signal activates at 0.2 mm ice accretion and stays on until after the end of the icing encounter through a manual trigger of the heater declared in the datalogger programming and will remain on for 25 seconds. Each time 0.2 mm forms on the probe, the event count is captured.

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.

Figure 1. MSO Circuit Schematic

Figure 2. MSO Circuit Sectional View

Section 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. It uses a MS27474T10B99PN connector (MIL-C-38999, series II, jam nut), containing seven 20-gauge pins. The unit weighs 0.7 lbs. (318 grams), maximum.

Figure 3. Physical Dimensions

Figure 4. Ice Detector

Section 5. Temperature Considerations

In the case of unit malfunction causing strut heater lock-on, the probe temperature can exceed

204.4°C (400°F). Maintenance personnel should exercise caution when servicing the unit.

Section 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.

6.1 Disconnection from Supply Source

The ice detector does not have an integrated power switch. The installation shall provide a switch or circuit breaker near the ice detector, within easy reach of the operator, and marked as the disconnecting device for the ice detector. The current rating for this switch or circuit breaker should be at least 1.9 Amps but not greater than 5 Amps.

6.2 Protection Against Electric Shock – External Circuit Connections

All external circuits are contained in one connector (see Section 4), so are not accessible when the unit and cable connectors are mated. Further, the operating voltages on all pins are externally produced and externally limited to less than 33 V relative to 28 VDC Return, so are not considered hazardous in normal or single fault conditions. All external circuits other than the Case Ground pin shall be insulated from the Case Ground pin and unit enclosure according to the dielectric and insulation requirements specified in Table 7-1.

Section 7. Mounting Considerations

Description

Colour

CR1000X/CR1000

CR6

RS-485 High

White

Control Port*

U Port*

RS-485 Low

Brown

Control Port*

U Port*

Case GND

Green G G

Figure 5. 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.

NOTE: The "Hot Surface" safety label should be visible to the operator after the equipment is installed. Otherwise, if the unit is installed fully enclosed, the mounting apparatus should include the safety label in a visible location.

Section 8. Wiring Diagram - using cable Part # 0871LP1CBL-L

Table 1. Datalogger Connections

24 VDC +

Red

V+

24 VDC -

Black

V-

*cannot share control ports

Table 2. Power Connections to C2673 (24VDC Power Supply)

‘

WARNING: Part C2673 must be installed by a certified electrician to local and national code.

Section 9. Program Example

9.1 CR1000X

Ice detector 0871LP1 Sensor

'==================Sensors and Peripherals===================== 'Sensor: , Ice detector 0871LP1, Output type RS485 , ' Polling Data' Baud rate: 9600, Data Bits: 8, Parity: None, Stop Bits: 1 The sensor will output Hex 24 Bytes string upon sending Command ' (S command to request current Satus and Command H to turn the heater ON) '======================Wiring============================== ' --------- Ice detector 0871LP1 -------------------------' All external circuits other than the Case Ground pin shall be insulated from the Case Ground pin and unit enclosure. ' RS485 port in the sensor: ' C5 ----------------------------- Brown (PIN E) RS-485 Low ' C6 ----------------------------- WHITE (PIN D) RS-485 High

' 24 V Power ---------------------Red (PIN A) ' Power Return ------------------ BLACK (PIN B) ' Earth Ground ------------------ Green ( PIN C) '=======================Constants========================= 'Start of Constants Customization Section 'Program Scan Rate Const Scan_Rate = 5 ' Ice thickness in mm Const Ice_mm_Threshold = 0.2 'End of Constants Customization Section '====================== Declarations========================

'Diagnostic Parameters

Public Battery_Voltage Units Battery_Voltage = Volts Public Panel_Temperature Units Panel_Temperature =Deg C

'0871LP1 Parameters

Public Read_LP1 As Boolean Public Ice Units Ice = inches Public Ice_mm Units Ice_mm = mm Public Ice_Event_Count As Long

Public LP1_Serial_Error As Boolean Dim LP1_Bytes(24) As Long Public LP1_String(24)As String Public LP1_Probe_Heater_State As String *3 Public LP1_Ice_Output As String *6

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