INSTRUCTION MANUAL 0871LH1 Freezing Rain Sensor November 2012 Copyright © 2007 Campbell Scientific (Canada)Corp.
TABLE OF CONTENTS 1 2 3 4 5 6 7 8 9 Purpose .............................................................................................................................................. 2 General............................................................................................................................................... 2 Detailed Principle of Operation ...........................................................................................................
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.
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.
4 Specifications Power Supply Operating Voltage: Power Draw: Temperature Operating: Storage: 18 – 29.
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).
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.
9 Wiring 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: Please contact a Certified Electrician to properly install the C2673 power supply. All electrical connections and housings must be installed by a Certified Electrician. 9 .1 0871LH1CBL-L Wiring for Discrete Output Table 2.
Figure 5 General Hook-up Diagram 9 .2 0871LH1CBL-L Wiring for RS422 Output 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. Table 4.
NOTE: WARNING: If the application requires the monitoring of the discrete outputs the 5Vdc connection must be made. Isolate wires that are not connected as they may cause problems if shorted to ground. Table 5. Power Connections to Terminal Expander Description Pin Colour Connection 24VDC A Red V+ 24VDC Return B Black V- Table 6.
Scan (5,Sec,0,0) '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.
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 sensor and output it to final storage.
'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
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
'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.
'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"
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_St
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.
• 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.
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.
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.
Byte 4 - ERRSTAT2 1 -2 MSO FREQUENCY 3 - ERRSTAT1 0 (First) 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7-6 0 1 Bit 7 (MSB) 6 5-3 2 Table 8.
7-0 7-0 7-4 3-0 7-4 3-0 MSO Frequency Fail Count Heater Fail Count Not Used Not Used See ERRSTAT1 Above See ERRSTAT2 Above See ERRSTAT1 Above See ERRSTAT2 Above See ERRSTAT1 Above See ERRSTAT2 Above Software Version per VDD/SC1 0.
Appendix B 1 Freezing Rain Sensor Block Diagram The block diagram in Figure 4: Functional Block Diagram provid understanding of the functionality of the freezing rain sensor.
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.
1 .6 Drive Coil The drive coil modulates the magnetic field of the magnetostrictive oscillator and causes an ultrasonic axial movement of the probe. 1.7 Feedback Coil The feedback coil senses the movement of the probe and when employed in the probe oscillator circuit, completes the feedback portion of the MSO. 1.8 Heater The probe heater de-ices the probe. It is activated when the nominal icing trip point of 0.
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.
3 Input/Output Specification 3 .1 Input/Output Pin Designations Table 10. Input/Output Pin Designations Input or Definition Output Signal Name Connector Pin 24VDC A Input 24VDC Return B Input Case Ground RS-422 High RS-422 Low Ice C D E F Input Output Output Output Current Wire Gauge 18-29.5 VDC** 1.5 Amp Max at 28VDC 20 ---- ---- 20 ------Per RS-422 Spec Per RS-422 Spec Per RS-422 Spec Per RS-422 Spec Ground Active (1.5V Max) 0.5 - 50 mA Open Inactive Status G Output Ground Inactive (1.
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