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Lightning Protection

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Section 7. Installation In laboratory applications, locating a stable earth ground is challenging, but still necessary. In older buildings, new ac receptacles on older ac wiring may indicate that a safety ground exists when, in fact, the socket is not grounded. If a safety ground does exist, good practice dictates the verification that it carries no current. If the integrity of the ac power ground is in doubt, also ground the system through the building plumbing, or use another verified connection to earth ground. Figure 33: Schematic of grounds 7.5.1.1 Lightning Protection The most common and destructive ESDs are primary and secondary lightning strikes. Primary lightning strikes hit instrumentation directly. Secondary strikes induce voltage in power lines or wires connected to instrumentation. While elaborate, expensive, and nearly infallible lightning protection systems are on the market, Campbell Scientific, for many years, has employed a simple and inexpensive design that protects most systems in most circumstances. It is, however, not infallible. 93

Section	Page
Revision and Copyright Information	1
Warranty	3
Assistance	5
Table of Contents	7
Section 1. Introduction	27
1.1 HELLO	27
1.2 Typography	27
Section 2. Cautionary Statements	29
Section 3. Initial Inspection	31
Section 4. Quickstart Tutorial	33
4.1 Primer – CR3000 Data-Acquisition	33
4.1.1 Components of a Data-Acquisition System	33
4.1.1.1 Sensors	33
4.1.1.2 Datalogger	33
4.1.1.3 Data Retrieval	33
4.1.2 CR3000 Module and Power Supply	34
4.1.2.1 Wiring Panel	34
4.1.2.2 Power Supply	35
4.1.2.3 Backup Battery	35
4.1.3 Sensors	36
4.1.3.1 Analog Sensors	36
4.1.3.2 Bridge Sensors	37
4.1.3.2.1 Voltage Excitation	38
4.1.3.2.2 Current Excitation	39
4.1.3.3 Pulse Sensors	39
4.1.3.3.1 Pulses Measured	39
4.1.3.3.2 Pulse-Input Channels	40
4.1.3.3.3 Pulse Sensor Wiring	40
4.1.3.4 RS-232 Sensors	41
4.1.4 Digital I/O Ports	42
4.1.5 SDM Channels	43
4.1.6 Input Expansion Modules	43
4.2 Hands-On: Measuring a Thermocouple	43
4.2.1 What You Will Need	43
4.2.2 Hardware Setup	44
4.2.2.1 Internal Power Supply	44
4.2.2.2 External Power Supply	44
4.2.3 PC200W Software Setup	45
4.2.4 Write Program with Short Cut	47
4.2.4.1 Procedure: (Short Cut Steps 1 to 6)	47
4.2.4.2 Procedure: (Short Cut Steps 7 to 9)	48
4.2.4.3 Procedure: (Short Cut Steps 10 to 11)	49
4.2.4.4 Procedure: (Short Cut Steps 12 to 16)	50
4.2.4.5 Procedure: (Short Cut Step 17 to 18)	51
4.2.5 Send Program and Collect Data	52
4.2.5.1 Procedure: (PC200W Step 1)	52
4.2.5.2 Procedure: (PC200W Steps 2 to 4)	52
4.2.5.3 Procedure: (PC200W Step 5)	53
4.2.5.4 Procedure: (PC200W Step 6)	53
4.2.5.5 Procedure: (PC200W Steps 7 to 9)	54
4.2.5.6 Procedure: (PC200W Steps 10 to 11)	55
4.2.5.7 Procedure: (PC200W Steps 12 to 13)	56
Section 5. System Overview	57
5.1 CR3000 Datalogger	58
5.1.1 Clock	59
5.1.2 Sensor Support	59
5.1.3 CR3000 Wiring Panel	60
5.1.3.1 Measurement Inputs	60
5.1.3.2 Voltage and Current Outputs	61
5.1.3.3 Grounding Terminals	62
5.1.3.4 Power Terminals	62
5.1.3.4.1 Power In	62
5.1.3.4.2 Power Out	62
5.1.3.5 Communications Ports	63
5.1.3.6 Integrated Keyboard Display	63
5.1.4 Power Requirements	64
5.1.5 Programming	65
5.1.5.1 Operating System and Settings	65
5.1.5.2 User Programming	65
5.1.6 Memory and Final Data Storage	66
5.1.7 Data Retrieval	67
5.1.7.1 Via Telecommunications	67
5.1.7.2 Via Mass-Storage Device	67
5.1.7.3 Via CF Card	67
5.1.7.4 Data File-Formats in CR3000 Memory	68
5.1.7.5 Data Format on Computer	68
5.1.8 Communications	68
5.1.8.1 PakBus	68
5.1.8.2 Modbus	69
5.1.8.3 DNP3 Communication	69
5.1.8.4 Keyboard Display	69
5.1.8.4.1 Custom Menus	69
5.1.9 Security	70
5.1.9.1 Vulnerabilities	71
5.1.9.2 Pass-code Lockout	72
5.1.9.2.1 Security By-Pass	73
5.1.9.3 Passwords	73
5.1.9.3.1 .csipasswd	73
5.1.9.3.2 PakBus Instructions	74
5.1.9.3.3 IS Instructions	74
5.1.9.3.4 Settings	74
5.1.9.4 File Encryption	74
5.1.9.5 Communications Encryption	75
5.1.9.6 Hiding Files	75
5.1.9.7 Signatures	75
5.1.10 Maintenance	75
5.1.10.1 Protection from Water	75
5.1.10.2 Protection from Voltage Transients	75
5.1.10.3 Calibration	76
5.1.10.4 Internal Battery	76
5.2 Datalogger Support Software	76
Section 6. CR3000 Specifications	79
Section 7. Installation	81
7.1 Moisture Protection	81
7.2 Temperature Range	81
7.3 Enclosures	81
7.4 Power Sources	82
7.4.1 CR3000 Power Requirement	83
7.4.2 Calculating Power Consumption	83
7.4.3 Power Supplies	83
7.4.3.1 External Batteries	83
7.4.3.2 Internal Batteries	84
7.4.3.2.1 Alkaline Battery Base	84
7.4.3.2.2 Sealed Rechargeable-Battery Base	85
7.4.3.2.3 Low Profile (No Battery) Base	88
7.4.4 Vehicle Power Connections	88
7.4.5 Powering Sensors and Devices	89
7.4.5.1 Switched Voltage Excitation	90
7.4.5.2 Switched Current Excitation	90
7.4.5.3 Continuous Regulated (5 Volt)	91
7.4.5.4 Continuous Analog Out (0 - 5 Volt)	91
7.4.5.5 Continuous Unregulated (Nominal 12 Volt)	91
7.4.5.6 Switched Unregulated (Nominal 12 Volt)	91
7.5 Grounding	92
7.5.1 ESD Protection	92
7.5.1.1 Lightning Protection	93
7.5.2 Single-Ended Measurement Reference	95
7.5.3 Ground Potential Differences	95
7.5.3.1 Soil Temperature Thermocouple	95
7.5.3.2 External Signal Conditioner	95
7.5.4 Ground Looping in Ionic Measurements	96
7.6 CR3000 Configuration	97
7.6.1 Device Configuration Utility	97
7.6.2 Sending the Operating System	98
7.6.2.1 Sending OS with DevConfig	99
7.6.2.2 Sending OS with Program Send	100
7.6.2.3 Sending OS with External Memory	101
7.6.3 Settings	101
7.6.3.1 Settings via DevConfig	101
7.6.3.1.1 Deployment Tab	103
7.6.3.1.2 Logger Control Tab	107
7.6.3.2 Settings via CRBasic	108
7.6.3.3 Durable Settings	108
7.6.3.3.1 \	109
7.6.3.3.2 Default.cr3 File	111
7.6.3.4 Program Run Priorities	111
7.6.3.5 Network Planner	112
7.6.3.5.1 Overview	112
7.6.3.5.2 Basics	113
7.7 Programming	114
7.7.1 Writing and Editing Programs	114
7.7.1.1 Short Cut Editor and Program Generator	114
7.7.1.2 CRBasic Editor	114
7.7.1.2.1 Inserting Comments into Program	115
7.7.2 Sending Programs	115
7.7.2.1 Preserving Data at Program Send	115
7.7.3 Syntax	117
7.7.3.1 Numerical Formats	117
7.7.3.2 Structure	117
7.7.3.3 Command Line	119
7.7.3.3.1 Multiple Statements on One Line	120
7.7.3.3.2 One Statement on Multiple Lines	120
7.7.3.4 Single-Line Declarations	120
7.7.3.4.1 Variables	120
7.7.3.4.2 Constants	127
7.7.3.4.3 Alias and Unit Declarations	129
7.7.3.5 Declared Sequences	130
7.7.3.5.1 Data Tables	130
7.7.3.5.2 Subroutines	137
7.7.3.5.3 Incidental Sequences	137
7.7.3.6 Execution and Task Priority	137
7.7.3.6.1 Pipeline Mode	138
7.7.3.6.2 Sequential Mode	139
7.7.3.7 Execution Timing	140
7.7.3.7.1 Scan() / NextScan	141
7.7.3.7.2 SlowSequence / EndSequence	142
7.7.3.7.3 SubScan() / NextSubScan	142
7.7.3.7.4 Scan Priorities in Sequential Mode	142
7.7.3.8 Instructions	144
7.7.3.8.1 Measurement and Data-Storage Processing	144
7.7.3.8.2 Argument Types	145
7.7.3.8.3 Names in Arguments	145
7.7.3.8.4 Expressions in Arguments	146
7.7.3.8.5 Arrays of Multipliers and Offsets	146
7.7.3.9 Expressions	147
7.7.3.9.1 Floating-Point Arithmetic	147
7.7.3.9.2 Mathematical Operations	148
7.7.3.9.3 Expressions with Numeric Data Types	148
7.7.3.9.4 Logical Expressions	150
7.7.3.9.5 String Expressions	152
7.7.3.10 Program Access to Data Tables	153
7.7.3.11 System Signatures	155
7.7.4 Tips	155
7.7.4.1 Use of Variable Arrays to Conserve Code Space	155
7.7.4.2 Use of Move() to Conserve Code Space	155
7.8 Programming Resource Library	156
7.8.1 Calibration Using FieldCal() and FieldCalStrain()	156
7.8.1.1 CAL Files	156
7.8.1.2 CRBasic Programming	156
7.8.1.3 Calibration Wizard Overview	157
7.8.1.4 Manual Calibration Overview	157
7.8.1.4.1 Single-Point Calibrations (zero, offset, or zero basis)	157
7.8.1.4.2 Two-point Calibrations (multiplier / gain)	158
7.8.1.5 FieldCal() Demonstration Programs	158
7.8.1.5.1 Zero or Tare (Option 0)	159
7.8.1.5.2 Offset (Option 1)	160
7.8.1.5.3 Zero Basis (Option 4)	162
7.8.1.5.4 Two-Point Slope and Offset (Option 2)	164
7.8.1.5.5 Two-Point Slope Only (Option 3)	166
7.8.1.6 FieldCalStrain() Demonstration Program	167
7.8.1.6.1 Quarter-Bridge Shunt (Option 13)	170
7.8.1.6.2 Quarter-Bridge Zero (Option 10)	170
7.8.2 Information Services	171
7.8.2.1 PakBus Over TCP/IP and Callback	172
7.8.2.2 Default HTTP Web Server	172
7.8.2.3 Custom HTTP Web Server	173
7.8.2.4 FTP Server	176
7.8.2.5 FTP Client	176
7.8.2.6 Telnet	176
7.8.2.7 SNMP	176
7.8.2.8 Ping	176
7.8.2.9 Micro-Serial Server	177
7.8.2.10 Modbus TCP/IP	177
7.8.2.11 DHCP	177
7.8.2.12 DNS	177
7.8.2.13 SMTP	177
7.8.3 SDI-12 Sensor Support	177
7.8.3.1 SDI-12 Transparent Mode	178
7.8.3.1.1 SDI-12 Transparent Mode Commands	179
7.8.3.2 SDI-12 Programmed Modes	182
7.8.3.2.1 SDI-12 Recorder Mode	182
7.8.3.2.2 SDI-12 Sensor Mode	189
7.8.3.3 SDI-12 Power Considerations	190
7.8.4 Subroutines	192
7.8.5 Wind Vector	193
7.8.5.1 OutputOpt Parameters	193
7.8.5.2 Wind Vector Processing	194
7.8.5.2.1 Measured Raw Data	195
7.8.5.2.2 Calculations	195
7.8.6 Custom Menus	198
7.8.7 Conditional Compilation	203
7.8.8 Serial I/O	205
7.8.8.1 Introduction	206
7.8.8.2 I/O Ports	207
7.8.8.3 Protocols	207
7.8.8.4 Glossary of Terms	208
7.8.8.5 CRBasic Programming	209
7.8.8.5.1 Input Instruction Set Basics	210
7.8.8.5.2 Input Programming Basics	211
7.8.8.5.3 Output Programming Basics	213
7.8.8.5.4 Translating Bytes	213
7.8.8.5.5 Memory Considerations	214
7.8.8.5.6 Demonstration Program	215
7.8.8.6 Testing Applications	216
7.8.8.6.1 Configure HyperTerminal	216
7.8.8.6.2 Create Send Text File	219
7.8.8.6.3 Create Text-Capture File	219
7.8.8.6.4 Serial Input Test Program	219
7.8.8.7 Q & A	225
7.8.9 TrigVar and DisableVar — Controlling Data Output and Processing	227
7.8.10 NSEC Data Type	228
7.8.10.1 NSEC Options	229
7.8.11 Bool8 Data Type	232
7.8.12 Faster Measurement Rates	236
7.8.12.1 Measurements from 1 Hz to 100 Hz	237
7.8.12.2 Measurement Rate: 101 to 600 Hz	238
7.8.12.2.1 SubScan() / NextSubScan Details	239
7.8.12.3 Measurement Rate: 601 to 2000 Hz	240
7.8.13 String Operations	241
7.8.13.1 String Operators	242
7.8.13.2 String Concatenation	242
7.8.13.3 String NULL Character	243
7.8.13.4 Inserting String Characters	244
7.8.13.5 Extracting String Characters	244
7.8.13.6 String Use of ASCII / ANSII Codes	244
7.8.13.7 Formatting Strings	245
7.8.13.8 Formatting String Hexadecimal Variables	245
7.8.14 Data Tables	245
7.8.15 PulseCountReset Instruction	246
7.8.16 Program Signatures	247
7.8.16.1 Text Signature	247
7.8.16.2 Binary Runtime Signature	247
7.8.16.3 Executable Code Signatures	247
7.8.17 Advanced Programming Examples	248
7.8.17.1 Miscellaneous Features	248
7.8.17.2 Running Average and Total of Rain	251
7.8.17.3 Use of Multiple Scans	251
7.8.17.4 Groundwater Pump Test	252
7.8.17.5 Scaling Array	255
7.8.17.6 Conditional Output	256
7.8.17.7 Capturing Events	257
7.8.18 PRT Measurement	258
7.8.18.1 PRT Calculation Standards	258
7.8.18.2 Measuring PT100s (100-Ohm PRTs)	262
7.8.18.2.1 Self-Heating and Resolution	262
7.8.18.2.2 PT100 in Four-Wire Half-Bridge	262
7.8.18.2.3 PT100 in Three-Wire Half-Bridge	265
7.8.18.2.4 PT100 in Four-Wire Full-Bridge	266
7.8.18.2.5 PT100s with Current Excitation	268
7.8.19 Running Average	271
7.8.20 Writing High-Frequency Data to CF	273
7.8.20.1 TableFile() with Option 64	274
7.8.20.2 TableFile() with Option 64 Replaces CardOut()	274
7.8.20.3 TableFile() with Option 64 Programming	274
7.8.20.4 Converting TOB3 Files with CardConvert	275
7.8.20.5 TableFile() with Option 64 Q & A	275
Section 8. Operation	279
8.1 Measurements	279
8.1.1 Time	279
8.1.1.1 Time Stamps	279
8.1.2 Voltage	280
8.1.2.1 Input Limits	281
8.1.2.2 Reducing Error	282
8.1.2.3 Measurement Sequence	283
8.1.2.4 Measurement Accuracy	284
8.1.2.5 Voltage Range	286
8.1.2.5.1 AutoRange	286
8.1.2.5.2 Fixed Voltage Ranges	286
8.1.2.5.3 Common Mode Null / Open Input Detect	287
8.1.2.6 Offset Voltage Compensation	287
8.1.2.6.1 Input and Excitation Reversal	288
8.1.2.6.2 Ground Reference Offset Voltage	289
8.1.2.6.3 Background Calibration	289
8.1.2.7 Integration	289
8.1.2.7.1 ac Power Line Noise Rejection	290
8.1.2.8 Signal Settling Time	291
8.1.2.8.1 Minimizing Settling Errors	292
8.1.2.8.2 Measuring the Necessary Settling Time	293
8.1.2.9 Self-Calibration	295
8.1.2.10 Time Skew Between Measurements	299
8.1.3 Resistance Measurements	300
8.1.3.1 ac Excitation	303
8.1.3.2 Accuracy of Ratiometric-Resistance Measurements	303
8.1.3.3 Strain Calculations	305
8.1.4 Thermocouple	306
8.1.4.1 Error Analysis	307
8.1.4.1.1 Panel-Temperature Error	307
8.1.4.1.2 Thermocouple Limits of Error	311
8.1.4.1.3 Thermocouple Voltage Measurement Error	312
8.1.4.1.4 Ground Looping Error	315
8.1.4.1.5 Noise Error	315
8.1.4.1.6 Thermocouple Polynomial Error	315
8.1.4.1.7 Reference-Junction Error	316
8.1.4.1.8 Thermocouple Error Summary	316
8.1.4.2 Use of External Reference Junction	317
8.1.5 Pulse	318
8.1.5.1 Pulse-Input Channels (P1 - P4)	320
8.1.5.1.1 High-frequency Pulse (P1 - P4)	320
8.1.5.1.2 Low-Level ac (P1 - P4)	321
8.1.5.1.3 Switch Closure (P1 - P4)	321
8.1.5.2 Pulse Input on Digital I/O Channels C1 - C8	321
8.1.5.2.1 High Frequency Mode	321
8.1.5.2.2 Low-Frequency Mode	322
8.1.5.3 Pulse Measurement Tips	322
8.1.5.3.1 Frequency Resolution	324
8.1.5.4 Pulse Measurement Problems	325
8.1.5.4.1 Pay Attention to Specifications	325
8.1.5.4.2 Input Filters and Signal Attenuation	325
8.1.5.4.3 Switch Bounce and NAN	327
8.1.6 Period Averaging	327
8.1.7 SDI-12 Recording	328
8.1.8 RS-232 and TTL	329
8.1.9 Field Calibration	329
8.1.10 Cabling Effects	329
8.1.10.1 Analog Sensor Cables	330
8.1.10.2 Sensors Requiring Current Excitation	330
8.1.10.3 Pulse Sensors	330
8.1.10.4 RS-232 Sensors	330
8.1.10.5 SDI-12 Sensors	330
8.1.11 Synchronizing Measurements	330
8.2 Measurement and Control Peripherals	332
8.2.1 Analog-Input Expansion Modules	332
8.2.2 Pulse-Input Expansion Modules	332
8.2.3 Serial-Input Expansion Modules	332
8.2.4 Control Outputs	333
8.2.4.1 Digital I/O Ports	333
8.2.4.2 Relays and Relay Drivers	333
8.2.4.3 Component-Built Relays	334
8.2.5 Analog Control / Output Devices	335
8.2.6 TIMs	335
8.2.7 Vibrating Wire	335
8.2.8 Low-level ac	335
8.3 Memory and Final Data Storage	335
8.3.1 Storage Media	335
8.3.1.1 Data Storage	338
8.3.1.1.1 Data Table SRAM	338
8.3.1.1.2 CPU: Drive	338
8.3.1.1.3 USR: Drive	338
8.3.1.1.4 USB: Drive	339
8.3.1.1.5 CRD: Drive	340
8.3.1.1.6 Data File Formats	341
8.3.2 Memory Conservation	344
8.3.3 Memory Reset	345
8.3.3.1 Full Memory Reset	345
8.3.3.2 Program Send Reset	345
8.3.3.3 Manual Data-Table Reset	345
8.3.3.4 Formatting Drives	345
8.3.4 File Management	346
8.3.4.1 File Attributes	347
8.3.4.2 Data Preservation	348
8.3.4.3 External Memory Power-up	348
8.3.4.3.1 Creating and Editing Powerup.ini	349
8.3.4.4 File Management Q & A	352
8.3.5 File Names	352
8.3.6 File System Errors	352
8.3.7 Memory Q & A	353
8.4 Telecommunications and Data Retrieval	354
8.4.1 Hardware and Carrier Signal	354
8.4.2 Protocols	355
8.4.3 Initiating Telecommunications (Callback)	355
8.5 PakBus Overview	356
8.5.1 PakBus Addresses	356
8.5.2 Nodes: Leaf Nodes and Routers	356
8.5.2.1 Router and Leaf-Node Configuration	357
8.5.3 Linking PakBus Nodes: Neighbor Discovery	358
8.5.3.1 Hello-message (two-way exchange)	359
8.5.3.2 Beacon (one-way broadcast)	359
8.5.3.3 Hello-request (one-way broadcast)	359
8.5.3.4 Neighbor Lists	359
8.5.3.5 Adjusting Links	359
8.5.3.6 Maintaining Links	360
8.5.4 PakBus Troubleshooting	360
8.5.4.1 Link Integrity	360
8.5.4.1.1 Automatic Packet-Size Adjustment	360
8.5.4.2 Ping	361
8.5.4.3 Traffic Flow	361
8.5.5 LoggerNet Network-Map Configuration	361
8.5.6 PakBus LAN Example	362
8.5.6.1 LAN Wiring	362
8.5.6.2 LAN Setup	363
8.5.6.3 LoggerNet Setup	366
8.5.7 PakBus Encryption	368
8.6 Alternate Telecommunications	369
8.6.1 DNP3	369
8.6.1.1 Overview	369
8.6.1.2 Programming for DNP3	369
8.6.1.2.1 Declarations	369
8.6.1.2.2 CRBasic Instructions	370
8.6.1.2.3 Programming for Data-Acquisition	371
8.6.2 Modbus	372
8.6.2.1 Overview	372
8.6.2.2 Terminology	372
8.6.2.2.1 Glossary of Terms	373
8.6.2.3 Programming for Modbus	374
8.6.2.3.1 Declarations	374
8.6.2.3.2 CRBasic Instructions - Modbus	374
8.6.2.3.3 Addressing (ModbusAddr)	375
8.6.2.3.4 Supported Function Codes (Function)	375
8.6.2.3.5 Reading Inverse-Format Registers	375
8.6.2.4 Troubleshooting	375
8.6.2.5 Modbus over IP	376
8.6.2.6 Modbus tidBytes	376
8.6.2.7 Converting 16-bit to 32-bit Longs	376
8.6.3 Web Service API	377
8.6.3.1 Authentication	377
8.6.3.2 Command Syntax	378
8.6.3.3 Time Syntax	380
8.6.3.4 Data Management	380
8.6.3.4.1 BrowseSymbols Command	380
8.6.3.4.2 DataQuery Command	384
8.6.3.5 Control	390
8.6.3.5.1 SetValueEx Command	390
8.6.3.6 Clock Functions	392
8.6.3.6.1 ClockSet Command	392
8.6.3.6.2 ClockCheck Command	394
8.6.3.7 Files Management	396
8.6.3.7.1 Sending a File to a Datalogger	396
8.6.3.7.2 FileControl Command	397
8.6.3.7.3 ListFiles Command	399
8.6.3.7.4 NewestFile Command	403
8.7 Support Software	404
8.8 Using the Keyboard Display	404
8.8.1 Data Display	407
8.8.1.1 Real-Time Tables and Graphs	408
8.8.1.2 Real-Time Custom	408
8.8.1.3 Final-Storage Tables	410
8.8.2 Run/Stop Program	411
8.8.3 File Display	412
8.8.3.1 File: Edit	412
8.8.4 PCCard (CF Card) Display	414
8.8.5 Ports and Status	414
8.8.6 Settings	415
8.8.6.1 Set Time / Date	415
8.8.6.2 PakBus Settings	415
8.8.7 Configure Display	416
8.9 Program and OS File Compression	416
8.10 CF Cards & Records Number	419
Section 9. Maintenance	421
9.1 Moisture Protection	421
9.2 Replacing the Internal Battery	421
9.3 Repair	424
Section 10. Troubleshooting	427
10.1 Status Table	427
10.2 Operating Systems	427
10.3 Programming	427
10.3.1 Status Table as Debug Resource	427
10.3.1.1 CompileResults	428
10.3.1.2 SkippedScan	429
10.3.1.3 SkippedSlowScan	429
10.3.1.4 SkippedRecord	429

Match case Limit results 1 per page

Section 7.

Installation

In laboratory applications, locating a stable earth ground is challenging, but still

necessary. In older buildings, new ac receptacles on older ac wiring may indicate

that a safety ground exists when, in fact, the socket is not grounded. If a safety

ground does exist, good practice dictates the verification that it carries no current.

If the integrity of the ac power ground is in doubt, also ground the system through

the building plumbing, or use another verified connection to earth ground.

Figure 33: Schematic of grounds

7.5.1.1 Lightning Protection

The most common and destructive ESDs are primary and secondary lightning

strikes. Primary lightning strikes hit instrumentation directly. Secondary strikes

induce voltage in power lines or wires connected to instrumentation. While

elaborate, expensive, and nearly infallible lightning protection systems are on the

market, Campbell Scientific, for many years, has employed a simple and

inexpensive design that protects most systems in most circumstances. It is,

however, not infallible.