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Offset Voltage

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Section 8. Operation Offset Voltage Summary In-Depth Measurement offset voltages are unavoidable, but can be minimized. Offset voltages originate with: • Ground currents • Seebeck effect • Residual voltage from a previous measurement Remedies include: • Connect power grounds to power ground terminals (G) • Use input reveral (RevDiff = True) with differential measurements • Automatic offset compensation for differential measurements when RevDiff = False • Automatic offset compensation for single-ended measurements when MeasOff = False • Better offset compensation when MeasOff = True • Excitation reversal (RevEx = True) • Longer settling times Voltage offset can be the source of significant error. For example, an offset of 3 μV on a 2500 mV signal causes an error of only 0.00012%, but the same offset on a 0.25 mV signal causes an error of 1.2%. The primary sources of offset voltage are ground currents and the Seebeck effect. Single-ended measurements are susceptible to voltage drop at the ground terminal caused by return currents from another device that is powered from the CR6 wiring panel, such as another manufacturer's telecommunication modem, or a sensor that requires a lot of power. Currents >5 mA are usually undesirable. The error can be avoided by routing power grounds from these other devices to a power ground G terminal on the CR6 wiring panel, rather than using a signal ground ( ) terminal. Ground currents can be caused by the excitation of resistive-bridge sensors, but these do not usually cause offset error. These currents typically only flow when a voltage excitation is applied. Return currents associated with voltage excitation cannot influence other single-ended measurements because the excitation is usually turned off before the CR6 moves to the next measurement. However, if the CRBasic program is written in such a way that an excitation terminal is enabled during an unrelated measurement of a small voltage, an offset error may occur. The Seebeck effect results in small thermally induced voltages across junctions of dissimilar metals as are common in electronic devices. Differential measurements are more immune to these than are single-ended measurements because of passive voltage cancelation occurring between matched high and low pairs such as U1/U2. So use differential measurements when measuring critical low-level voltages, especially those below 200 mV, such as are output from pyranometers and thermocouples. Differential measurements also have the advantage of an input reversal option, RevDiff. When RevDiff is True, two differential measurements are made, the first with a positive polarity and the second reversed. Subtraction of opposite polarity measurements cancels some offset voltages associated with the measurement. 323

Section	Page
Revision and Copyright Information	1
Warranty	3
Assistance	5
Table of Contents	7
1. Introduction	29
1.1 HELLO	29
1.2 Typography	29
1.3 Capturing CRBasic Code	30
1.4 Release Notes	30
2. Cautionary Statements	31
3. Initial Inspection	33
4. System Quickstart	35
4.1 Data-Acquisition Systems — Quickstart	35
4.2 Sensors — Quickstart	36
4.3 Datalogger — Quickstart	37
4.3.1.1 Wiring Panel — Quickstart	37
4.4 Power Supplies — Quickstart	38
4.4.1 Internal Battery — Quickstart	39
4.5 Data Retrieval and Telecommunications — Quickstart	39
4.6 Datalogger Support Software — Quickstart	40
4.7 Tutorial: Measuring a Thermocouple	40
4.7.1 What You Will Need	40
4.7.2 Hardware Setup	41
4.7.2.1 External Power Supply	41
4.7.3 PC200W Software Setup	41
4.7.4 Write CRBasic Program with Short Cut	43
4.7.4.1 Procedure: (Short Cut Steps 1 to 5)	43
4.7.4.2 Procedure: (Short Cut Steps 6 to 7)	44
4.7.4.3 Procedure: (Short Cut Step 8)	45
4.7.4.4 Procedure: (Short Cut Steps 9 to 12)	46
4.7.4.5 Procedure: (Short Cut Steps 13 to 14)	47
4.7.5 Send Program and Collect Data	48
4.7.5.1 Procedure: (PC200W Step 1)	48
4.7.5.2 Procedure: (PC200W Steps 2 to 4)	48
4.7.5.3 Procedure: (PC200W Step 5)	49
4.7.5.4 Procedure: (PC200W Step 6)	50
4.7.5.5 Procedure: (PC200W Steps 7 to 10)	51
4.7.5.6 Procedure: (PC200W Steps 11 to 12)	52
4.7.5.7 Procedure: (PC200W Steps 13 to 14)	52
5. System Overview	55
5.1 Measurements — Overview	56
5.1.1 Time Keeping — Overview	57
5.1.2 Analog Measurements — Overview	57
5.1.2.1 Voltage Measurements — Overview	57
5.1.2.1.1 Single-Ended Measurements — Overview	59
5.1.2.1.2 Differential Measurements — Overview	60
5.1.2.2 Current Measurements — Overview	60
5.1.2.3 Resistance Measurements — Overview	60
5.1.2.3.1 Voltage Excitation	61
5.1.2.3.2 Current Excitation	63
5.1.2.4 Strain Measurements — Overview	64
5.1.3 Pulse Measurements — Overview	64
5.1.3.1 Pulses Measured	64
5.1.3.2 Pulse-Input Channels	65
5.1.3.3 Pulse Sensor Wiring	65
5.1.4 Period Averaging — Overview	66
5.1.5 Vibrating-Wire Measurements — Overview	67
5.1.5.1 Quickstart	68
5.1.6 Reading Smart Sensors — Overview	68
5.1.6.1 SDI-12 Sensor Support — Overview	69
5.1.6.2 RS-232 — Overview	69
5.1.6.3 RS-485 — Overview -- 6	70
5.1.7 Field Calibration — Overview	70
5.1.8 Cabling Effects — Overview	71
5.1.9 Synchronizing Measurements — Overview	71
5.2 Datalogger — Overview	71
5.2.1 Time Keeping — Overview	72
5.2.2 Wiring Panel — Overview	72
5.2.2.1 Switched Voltage Output — Overview	75
5.2.2.2 Voltage and Current Excitation — Overview	75
5.2.2.3 Grounding Terminals	76
5.2.2.4 Power Terminals	76
5.2.2.4.1 Power In	76
5.2.2.4.2 Power Out Terminals	76
5.2.2.5 Communication Ports	77
5.2.2.5.1 CS I/O Port	77
5.2.2.5.2 RS-232 Ports	78
5.2.2.5.3 USB Port	78
5.2.2.5.4 Micro SD Card Slot	78
5.2.2.5.5 SDI-12 Ports	78
5.2.2.5.6 SDM Port	78
5.2.2.5.7 CPI Port	78
5.2.2.5.8 Ethernet Port	79
5.2.3 Keyboard Display — Overview	79
5.2.3.1 Character Set	79
5.2.3.2 Custom Menus — Overview	80
5.2.4 Measurement and Control Peripherals — Overview	81
5.2.5 Power Supplies — Overview	81
5.2.6 CR6 Configuration — Overview	82
5.2.7 CRBasic Programming — Overview	82
5.2.8 Memory — Overview	83
5.2.9 Data Retrieval and Telecommunications — Overview	84
5.2.9.1 PakBus — Overview	84
5.2.9.2 Telecommunications	85
5.2.9.3 Mass-Storage Device	85
5.2.9.4 Micro SD Card	85
5.2.9.5 Data-File Formats in CR6 Memory	86
5.2.9.6 Data Format on Computer	86
5.2.10 Alternate Telecommunications — Overview	86
5.2.10.1 Modbus	86
5.2.10.2 DNP3 — Overview	87
5.2.10.3 Web API — Overview	87
5.2.11 Security — Overview	87
5.2.12 Maintenance — Overview	88
5.2.12.1 Protection from Water	88
5.2.12.2 Protection from Voltage Transients	88
5.2.12.3 Calibration	88
5.2.12.4 Internal Battery — Details	88
5.3 Datalogger Support Software — Overview	89
6. CR6 Specifications	91
6.1 Voltage Measurements — Specifications	91
6.2 Resistance Measurements — Specifications	93
6.3 Voltage and Current Excitation — Specifications	93
6.4 Vibrating-Wire Measurements — Specifications	94
6.5 Thermistor Measurements — Specifications	95
6.6 Period Averaging — Specifications	95
6.7 Pulse Measurements — Specifications	96
6.8 Switched Voltage Output — Specifications	97
6.9 Total System Current — Specifications	98
6.10 Communications — Specifications	98
6.11 System — Specifications	99
6.12 Power Supplies — Specifications	100
6.13 Compliance — Specifications	100
6.14 Physical Attributes — Specifications	101
7. Installation	103
7.1 Moisture Protection	103
7.2 Temperature Range	103
7.3 Enclosures	103
7.4 Power Supplies — Details	104
7.4.1 CR6 Power Requirement	105
7.4.2 Calculating Power Consumption	105
7.4.3 Power Sources	105
7.4.3.1 Uninterruptable Power Supply (UPS)	106
7.4.4 Vehicle Power Connections	107
7.5 Switched Voltage Output — Details	107
7.5.1 Switched-Voltage Excitation	109
7.5.2 Switched Current Excitation	109
7.5.3 Continuous Unregulated Voltage (12V Terminal)	109
7.5.4 Switched Unregulated Voltage (SW12 Terminal)	109
7.6 Grounding	110
7.6.1 ESD Protection	110
7.6.1.1 Lightning Protection	111
7.6.2 Single-Ended Measurement Reference	113
7.6.3 Ground-Potential Differences	114
7.6.3.1 Soil Temperature Thermocouple	114
7.6.3.2 External Signal Conditioner	114
7.6.4 Ground Looping in Ionic Measurements	114
7.7 CR6 Configuration — Details	115
7.7.1 Device Configuration Utility	116
7.7.2 Sending the Operating System (OS)	117
7.7.2.1 Sending OS with DevConfig	118
7.7.2.2 Sending OS with Program Send	119
7.7.2.3 Sending OS with External Memory	119
7.7.3 Settings	120
7.7.4 Durable Settings	120
7.7.4.1 'Include' File	120
7.7.4.2 Default.CR6 File	124
7.7.5 Program Run Priorities	124
7.7.6 Network Planner	125
7.7.6.1 Overview	125
7.7.6.2 Basics	126
7.8 CRBasic Programming — Details	126
7.8.1 Writing and Editing Programs	127
7.8.1.1 Short Cut Programming Wizard	127
7.8.1.2 CRBasic Editor	127
7.8.1.2.1 Inserting Comments into Program	128
7.8.1.2.2 Conserving Program Memory	128
7.8.2 Sending Programs	128
7.8.2.1 Preserving Data at Program Send	129
7.8.3 Syntax	130
7.8.3.1 Numerical Formats	130
7.8.3.2 Program Structure	131
7.8.3.3 Command Line	133
7.8.3.3.1 Multiple Statements on One Line	133
7.8.3.3.2 One Statement on Multiple Lines	134
7.8.3.4 Single-Line Declarations	134
7.8.3.4.1 Variables	134
7.8.3.4.2 Constants	143
7.8.3.4.3 Alias and Unit Declarations	143
7.8.3.5 Declared Sequences	144
7.8.3.5.1 Data Tables	144
7.8.3.5.2 Subroutines	152
7.8.3.5.3 Incidental Sequences	152
7.8.3.6 Execution and Task Priority	152
7.8.3.6.1 Pipeline Mode	153
7.8.3.6.2 Sequential Mode	154
7.8.3.7 Execution Timing	155
7.8.3.7.1 Scan() / NextScan	156
7.8.3.7.2 SlowSequence / EndSequence	157
7.8.3.7.3 SubScan() / NextSubScan	157
7.8.3.7.4 Scan Priorities in Sequential Mode	157
7.8.3.8 Instructions	159
7.8.3.8.1 Measurement and Data-Storage Processing	159
7.8.3.8.2 Argument Types	160
7.8.3.8.3 Names in Arguments	160
7.8.3.9 Expressions in Arguments	161
7.8.3.10 Expression Types	161
7.8.3.10.1 Floating-Point Arithmetic	162
7.8.3.10.2 Mathematical Operations	162
7.8.3.10.3 Expressions with Numeric Data Types	162
7.8.3.10.4 Logical Expressions	164
7.8.3.10.5 String Expressions	167
7.8.3.11 Program Access to Data Tables	168
7.8.3.12 System Signatures	170
7.9 Programming Resource Library	170
7.9.1 Advanced Programming Techniques	170
7.9.1.1 Capturing Events	170
7.9.1.2 Conditional Output	171
7.9.1.3 Groundwater Pump Test	172
7.9.1.4 Miscellaneous Features	175
7.9.1.5 PulseCountReset Instruction	177
7.9.1.6 Scaling Array	178
7.9.1.7 Signatures: Example Programs	179
7.9.1.7.1 Text Signature	179
7.9.1.7.2 Binary Runtime Signature	179
7.9.1.7.3 Executable Code Signatures	179
7.9.1.8 Use of Multiple Scans	180
7.9.2 Compiling: Conditional Inclusion of Code Segments	181
7.9.3 Data Displays: Custom Menus — Details	183
7.9.4 Data Input: Loading Large Data Sets	188
7.9.5 Data Input: Array-Assigned Expression	189
7.9.6 Data Output: Calculating Running Average	193
7.9.7 Data Output: Triggers and Omitting Samples	195
7.9.8 Data Output: Two Intervals in One Data Table	197
7.9.9 Data Output: Using Data Type Bool8	198
7.9.10 Data Output: Using Data Type NSEC	202
7.9.10.1 NSEC Options	203
7.9.11 Data Output: Writing High-Frequency Data to Memory Cards	206
7.9.11.1 TableFile() with Option 64	206
7.9.11.2 TableFile() with Option 64 Replaces CardOut()	207
7.9.11.3 TableFile() with Option 64 Programming	207
7.9.11.4 TableFile() with Option 64 Q & A	208
7.9.12 Field Calibration — Details	210
7.9.12.1 Field Calibration CAL Files	211
7.9.12.2 Field Calibration Programming	211
7.9.12.3 Field-Calibration Wizard Overview	211
7.9.12.4 Field Calibration Keyboard Procedures	212
7.9.12.4.1 One-Point Calibrations (zero or offset)	212
7.9.12.4.2 Two-Point Calibrations (gain and offset)	213
7.9.12.4.3 Zero Basis Point Calibration	213
7.9.12.5 FieldCal() Examples	213
7.9.12.5.1 FieldCal() Zero or Tare (Opt 0) Example	214
7.9.12.5.2 FieldCal() Offset (Opt 1) Example	216
7.9.12.5.3 FieldCal() Slope and Offset (Opt 2) Example	218
7.9.12.5.4 FieldCal() Slope (Opt 3) Example	221
7.9.12.5.5 Zero Basis (Option 4)	223
7.9.12.6 FieldCalStrain() Examples	225
7.9.12.6.1 FieldCalStrain() Quarter-Bridge Shunt Example	228
7.9.12.6.2 FieldCalStrain() Quarter-Bridge Zero	228
7.9.13 Measurement: Excite, Delay, Measure	229
7.9.14 Measurement: Faster Analog Rates	230
7.9.14.1 Measurements from 1 to 100 Hz	231
7.9.14.2 Measurement Rate: 101 to 600 Hz	232
7.9.14.2.1 Measurements from 101 to 600 Hz 2	233
7.9.14.3 Measurement Rate: 601 to 2000 Hz	234
7.9.15 Measurement: PRT	235
7.9.15.1 PRT Calculation Standards	235
7.9.15.2 Measuring PT100s (100 Ω PRTs)	239
7.9.15.2.1 Self-Heating and Resolution	239
7.9.15.2.2 PT100 in Four-Wire Half-Bridge	239
7.9.15.2.3 PT100 in Three-Wire Half Bridge	242
7.9.15.2.4 PT100 in Four-Wire Full-Bridge	243
7.9.15.2.5 PT100 with Current Excitation	245
7.9.16 Serial I/O: Capturing Serial Data	248
7.9.16.1 Introduction	248
7.9.16.2 I/O Ports	249
7.9.16.3 Protocols	250
7.9.16.4 Glossary of Serial I/O Terms	250
7.9.16.5 CRBasic Programming	252
7.9.16.5.1 Input Instruction Set Basics	252
7.9.16.5.2 Input Programming Basics	253
7.9.16.5.3 Output Programming Basics	255
7.9.16.5.4 Translating Bytes	255
7.9.16.5.5 Memory Considerations	256
7.9.16.5.6 Demonstration Program	257
7.9.16.6 Testing Applications	258
7.9.16.6.1 Configure HyperTerminal	258
7.9.16.6.2 Create Send Text File	261
7.9.16.6.3 Create Text-Capture File	261
7.9.16.6.4 Serial Input Test Program	261
7.9.16.7 Q & A	267
7.9.17 Serial I/O: SDI-12 Sensor Support — Details	269
7.9.17.1 SDI-12 Transparent Mode	269
7.9.17.1.1 SDI-12 Transparent Mode Commands	270
7.9.17.2 SDI-12 Programmed Modes	274
7.9.17.2.1 SDI-12 Recorder Mode	274
7.9.17.2.2 SDI-12 Sensor Mode	281
7.9.17.3 SDI-12 Power Considerations	283
7.9.18 String Operations	284
7.9.18.1 String Operators	284
7.9.18.2 String Concatenation	285
7.9.18.3 String NULL Character	287
7.9.18.4 Inserting String Characters	288
7.9.18.5 Extracting String Characters	288
7.9.18.6 String Use of ASCII / ANSII Codes	288
7.9.18.7 Formatting Strings	288
7.9.18.8 Formatting String Hexadecimal Variables	289
7.9.19 Subroutines	289
7.9.20 Web Services	291
7.9.20.1 PakBus Over TCP/IP and Callback	292
7.9.20.2 Default HTTP Web Server	292
7.9.20.3 Custom HTTP Web Server	293
7.9.20.4 FTP Server	296
7.9.20.5 FTP Client	296
7.9.20.6 Telnet	296
7.9.20.7 SNMP	296
7.9.20.8 Ping (IP)	297
7.9.20.9 Micro-Serial Server	297
7.9.20.10 Modbus TCP/IP	297
7.9.20.11 DHCP	297
7.9.20.12 DNS	297
7.9.20.13 SMTP	297
7.9.20.14 HTTPS	297
7.9.21 Wind Vector	298
7.9.21.1 OutputOpt Parameters	298
7.9.21.2 Wind Vector Processing	299
7.9.21.2.1 Measured Raw Data	299
7.9.21.2.2 Calculations	300
8. Operation	305
8.1 Measurements — Details	305
8.1.1 Time Keeping — Details	305
8.1.1.1 Time Stamps	305
8.1.2 Analog Measurements — Details	307
8.1.2.1 Voltage Measurements — Details	307
8.1.2.1.1 Voltage Measurement Mechanics	307
8.1.2.1.2 Voltage Measurement Limitations	310
8.1.2.1.3 Voltage Measurement Quality	312
8.1.2.2 Thermocouple Measurements	328
8.1.2.3 Current Measurements — Details	329
8.1.2.4 Resistance Measurements — Details	329
8.1.2.4.1 Ac Excitation	334
8.1.2.4.2 Resistance Measurements — Accuracy	335
8.1.2.5 Strain Measurements — Details	336
8.1.3 Pulse Measurements — Details	337
8.1.3.1 Terminal Specific Application Notes	340
8.1.3.2 Low-Level Ac Measurements	340
8.1.3.3 High-Frequency Measurements	341
8.1.3.3.1 Frequency Resolution	341
8.1.3.3.2 Frequency Measurement Q & A	342
8.1.3.4 Switch-Closure and Open-Collector Measurements	343
8.1.3.5 Edge Timing	343
8.1.3.6 Edge Counting	344
8.1.3.7 Pulse Measurement Tips	344
8.1.3.7.1 Pay Attention to Specifications	345
8.1.3.7.2 Input Filters and Signal Attenuation	345
8.1.4 Period Averaging — Details	346
8.1.5 Vibrating-Wire Measurements — Details	347
8.1.5.1 Vspect Measurements	348
8.1.5.1.1 Quickstart	349
8.1.5.1.2 Static Vspect Measurement Theory	350
8.1.5.1.3 Vspect Connections	357
8.1.5.1.4 Vspect Programming	357
8.1.6 Reading Smart Sensors — Details	365
8.1.6.1 SDI-12 Recording	365
8.1.6.2 RS-232 and TTL	366
8.1.7 Field Calibration — Overview	366
8.1.8 Cabling Effects	367
8.1.8.1 Analog-Sensor Cables	367
8.1.8.2 Sensors Requiring Current Excitation	367
8.1.8.3 Pulse Sensors	367
8.1.8.4 RS-232 Sensors	367
8.1.8.5 SDI-12 Sensors	367
8.1.9 Synchronizing Measurements	368
8.2 Measurement and Control Peripherals — Details	369
8.2.1 Analog-Input Modules	369
8.2.2 Pulse-Input Modules	370
8.2.2.1 Low-Level Ac	370
8.2.3 Serial I/O Modules — Details	370
8.2.4 Terminal-Input Modules	370
8.2.5 Vibrating-Wire Modules	370
8.2.6 Analog-Output Modules	370
8.2.7 Control-Output Modules	371
8.2.7.1 Terminals Configured for Control	371
8.2.7.2 Relays and Relay Drivers	371
8.2.7.3 Component-Built Relays	372
8.3 Memory	373
8.3.1 Storage Media	373
8.3.1.1 Data Storage — On-board	376
8.3.1.1.1 Data Table SRAM	376
8.3.1.1.2 CPU: Drive	376
8.3.1.1.3 USR: Drive	376
8.3.1.1.4 USB: Drive	377
8.3.1.1.5 CRD: Drive	378
8.3.1.1.6 Data-File Formats	379
8.3.2 Memory Reset	383
8.3.2.1 Full Memory Reset	383
8.3.2.2 Program Send Reset	383
8.3.2.3 Manual Data-Table Reset	383
8.3.2.4 Formatting Drives	383
8.3.3 File Management	384
8.3.3.1 File Attributes	385
8.3.3.2 Files Manager	386
8.3.3.3 Data Preservation	387
8.3.3.4 External Memory Power-up	387
8.3.3.4.1 Creating and Editing Powerup.ini	388
8.3.3.5 File Management Q & A	391
8.3.4 File Names	391
8.3.5 File System Errors	391
8.3.6 Memory Q & A	392
8.4 Data Retrieval and Telecommunications — Details	393
8.4.1 Protocols	393
8.4.2 Conserving Bandwidth	393
8.4.3 Initiating Telecommunications (Callback)	394
8.5 PakBus — Details	395
8.5.1 PakBus Addresses	395
8.5.2 Nodes: Leaf Nodes and Routers	395
8.5.2.1 Router and Leaf-Node Configuration	396
8.5.3 Linking PakBus Nodes: Neighbor Discovery	397
8.5.3.1 Hello-Message	398
8.5.3.2 Beacon	398
8.5.3.3 Hello-Request	398
8.5.3.4 Neighbor Lists	398
8.5.3.5 Adjusting Links	398
8.5.3.6 Maintaining Links	398
8.5.4 PakBus Troubleshooting	399
8.5.4.1 Link Integrity	399
8.5.4.1.1 Automatic Packet-Size Adjustment	399
8.5.4.2 Ping (PakBus)	400
8.5.4.3 Traffic Flow	400
8.5.5 LoggerNet Network-Map Configuration	400
8.5.6 PakBus LAN Example	402
8.5.6.1 LAN Wiring	402
8.5.6.2 LAN Setup	402
8.5.6.3 LoggerNet Setup	405
8.5.7 Route Filters	406
8.5.8 PakBusRoutes	406
8.5.9 Neighbors	407
8.5.10 PakBus Encryption	408
8.6 Alternate Telecommunications — Details	409
8.6.1 iBus	409
8.6.2 DNP3 — Details	409
8.6.2.1 DNP3 Introduction	409
8.6.2.2 Programming for DNP3	410
8.6.2.2.1 Declarations (DNP3 Programming)	410
8.6.2.2.2 CRBasic Instructions (DNP3)	411
8.6.2.2.3 Programming for DNP3 Data Acquisition	411
8.6.3 Modbus — Details	413
8.6.3.1 Modbus Terminology	414
8.6.3.1.1 Glossary of Modbus Terms	414
8.6.3.2 Programming for Modbus	415
8.6.3.2.1 Declarations (Modbus Programming)	415
8.6.3.2.2 CRBasic Instructions (Modbus)	415
8.6.3.2.3 Addressing (ModbusAddr)	416
8.6.3.2.4 Supported Modbus Function Codes	416
8.6.3.2.5 Reading Inverse-Format Modbus Registers	416
8.6.3.3 Troubleshooting (Modbus)	417
8.6.3.4 Modbus over IP	417
8.6.3.5 Modbus Q and A	417
8.6.3.6 Converting Modbus 16-Bit to 32-Bit Longs	417
8.6.4 Web API — Details	418
8.6.4.1 Authentication	419
8.6.4.2 Command Syntax	419
8.6.4.3 Time Syntax	421
8.6.4.4 Data Management	422
8.6.4.4.1 BrowseSymbols Command	422
8.6.4.4.2 DataQuery Command	425
8.6.4.5 Control	431
8.6.4.5.1 SetValueEx Command	431
8.6.4.6 Clock Functions	433
8.6.4.6.1 ClockSet Command	433
8.6.4.6.2 ClockCheck Command	435
8.6.4.7 Files Management	437
8.6.4.7.1 Sending a File to a Datalogger	437
8.6.4.7.2 FileControl Command	438
8.6.4.7.3 ListFiles Command	440
8.6.4.7.4 NewestFile Command	444
8.7 Datalogger Support Software — Details	445
8.8 Keyboard Display — Details	446
8.8.1 Data Display	448
8.8.1.1 Real-Time Tables and Graphs	449
8.8.1.2 Real-Time Custom	449
8.8.1.3 Final-Memory Tables	451
8.8.2 Run/Stop Program	452
8.8.3 File Display	453
8.8.3.1 File: Edit	453
8.8.4 PCCard (Memory Card) Display	455
8.8.5 Ports and Status	455
8.8.6 Settings	456
8.8.6.1 Set Time / Date	456
8.8.6.2 PakBus Settings	456
8.8.7 Configure Display	457
8.9 Memory Cards and Record Numbers	457
8.10 CPI Bus and CDM Devices	458
8.11 Security — Details	458
8.11.1 Vulnerabilities	459
8.11.2 Pass-Code Lockout	460
8.11.2.1 Pass-Code Lockout By-Pass	461
8.11.3 Passwords	461
8.11.3.1 .csipasswd	462
8.11.3.2 PakBus Instructions	462
8.11.3.3 TCP/IP Instructions	462
8.11.3.4 Settings	462
8.11.4 File Encryption	462
8.11.5 Communication Encryption	463
8.11.6 Hiding Files	463
8.11.7 Signatures	463
9. Maintenance — Details	465
9.1 Moisture Protection	465
9.2 Replacing the Internal Battery	465
9.2.1 Replacing the Internal Battery	466

Match case Limit results 1 per page

Section 8.

Operation

Offset Voltage

Measurement offset voltages are unavoidable, but can be minimized.

Summary

Offset voltages originate with:

•

Ground currents

•

Seebeck effect

•

Residual voltage from a previous measurement

Remedies include:

•

Connect power grounds to power ground terminals (

)

•

Use input reveral (

RevDiff

True

) with differential measurements

•

Automatic offset compensation for differential measurements when

RevDiff

False

•

Automatic offset compensation for single-ended measurements when

MeasOff

False

•

Better offset compensation when

MeasOff

True

•

Excitation reversal (

RevEx

True

)

•

Longer settling times

In-Depth

Voltage offset can be the source of significant error.

For example, an offset of 3

μV on a 2500 mV signal causes an error of only 0.00012%, but the same offset on

a 0.25 mV signal causes an error of 1.2%.

The primary sources of offset voltage

are ground currents and the Seebeck effect.

Single-ended measurements are susceptible to voltage drop at the ground terminal

caused by return currents from another device that is powered from the CR6

wiring panel, such as another manufacturer's telecommunication modem, or a

sensor that requires a lot of power.

Currents >5 mA are usually undesirable.

The

error can be avoided by routing power grounds from these other devices to a

power ground

terminal on the CR6 wiring panel, rather than using a signal

ground (

) terminal.

Ground currents can be caused by the excitation of

resistive-bridge sensors, but these do not usually cause offset error.

These

currents typically only flow when a voltage excitation is applied.

Return currents

associated with voltage excitation cannot influence other single-ended

measurements because the excitation is usually turned off before the CR6 moves

to the next measurement.

However, if the CRBasic program is written in such a

way that an excitation terminal is enabled during an unrelated measurement of a

small voltage, an offset error may occur.

The Seebeck effect results in small thermally induced voltages across junctions of

dissimilar metals as are common in electronic devices.

Differential measurements

are more immune to these than are single-ended measurements because of passive

voltage cancelation occurring between matched high and low pairs such as

So use differential measurements when measuring critical low-level

voltages, especially those below 200 mV, such as are output from pyranometers

and thermocouples.

Differential measurements also have the advantage of an

input reversal option,

RevDiff

When

RevDiff

True

, two differential

measurements are made, the first with a positive polarity and the second reversed.

Subtraction of opposite polarity measurements cancels some offset voltages

associated with the measurement.

323