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Bridge Resistance Measurements

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Section 4. Sensor Support 4.2.5 Self-Calibration A calibration measurement to measure the ground offset is made at the beginning of each measurement instruction that includes a voltage measurement. This calibration takes about 400 microseconds. Only one calibration measurement is made per instruction regardless of the number of reps. The battery voltage is checked every 8 seconds to ensure it is within the allowable range. 4.3 Bridge Resistance Measurements Many sensors detect phenomena by way of change in a resistive circuit. Thermistors, strain gages, and position potentiometers are examples. Resistance measurements are special case voltage measurements. By supplying a precise, known voltage to a resistive circuit, then measuring the returning voltage, resistance can be calculated. Two bridge measurement instructions are included in the CR200(X), ExDelSE () and Therm109 (). ExDelSE () is used with sensors that have a simple half bridge circuit. Therm109 () is used with Campbell Scientific's 109-L thermistor probe. Sensors with bridge circuits that require a differential voltage measurement, such as full bridge or 3-wire half bridge, cannot be measured with the CR200(X). FIGURE. Half Bridge Circuit Used with ExDelSE (p. 41) shows the circuit that is typically measured with ExDelSE (). In the diagram. Rs is normally the sensor and Rf is normally a precision fixed (static) resistor. Vx is the excitation voltage (either 2500 or 5000 mV) and V1 is the voltage (mV) measured by the analog input channel. Calculating the resistance of a sensor that is one of the legs of a resistive bridge requires additional processing following the bridge measurement instruction. FIGURE. Half Bridge Circuit Used with ExDelSE (p. 41) lists the schematics of a typical half bridge configuration and the calculations necessary to compute the resistance of any single resistor, provided the value of the other resistor in the bridge circuit is known. Figure 28: Voltage Excitation Bridge Circuit 41

Section	Page
Revision and Copyright Information	1
Warranty	3
Assistance	4
Table of Contents	5
Section 1. Introduction	13
1.1 CR200(X) series Datalogger Models	13
Section 2. Quickstart Tutorial	15
2.1 Primer - CR200(X) Data Acquisition	15
2.1.1 Components of a Data Acquisition System	15
2.1.1.1 How Programmed Instructions Are Evaluated	15
2.1.1.2 Sensors	15
2.1.1.3 Datalogger	16
2.1.1.4 Data Retrieval	16
2.1.2 CR200(X) Mounting	16
2.1.3 Wiring Panel	16
2.1.4 Battery Backup	17
2.1.5 Power Supply	17
2.1.6 Antenna	17
2.1.7 Analog Sensors	18
2.1.8 Bridge Sensors	18
2.1.8.1 Voltage Excitation	18
2.1.9 Pulse Sensors	19
2.1.10 Digital I/O Ports	20
2.1.11 RS-232 Sensors	21
2.2 Hands-on Exercise - Measuring Temperature	22
2.2.1 Hardware Setup	23
2.2.2 Configuration	23
2.2.3 PC200W Software Setup	23
2.2.3.1 Programming With Short Cut	25
2.2.3.1.1 Short Cut Programming Objectives	25
2.2.3.1.2 Procedure (Short Cut Steps 1–6)	25
2.2.3.1.3 Procedure (Short Cut Steps 7–9)	26
2.2.3.1.4 Procedure (Short Cut Step 10)	27
2.2.3.1.5 Procedure (Short Cut Step 11)	27
2.2.3.1.6 Procedure (Short Cut Steps 12 –18)	28
2.2.3.1.7 Procedure (Short Cut Step 19)	29
2.2.3.1.8 Procedure (Short Cut Step 20)	29
2.2.3.2 Programming the CR200(X) and Collecting Data	30
2.2.3.2.1 Procedure (PC200W Step 1)	30
2.2.3.2.2 Procedure (PC200W Steps 2–4)	30
2.2.3.2.3 Procedure (PC200W Step 5)	31
2.2.3.2.4 Procedure (PC200W Step 6)	31
2.2.3.2.5 Procedure (PC200W Steps 7–9)	32
2.2.3.2.6 Procedure (PC200W Step 10)	33
2.2.3.2.7 Procedure (PC200W Step 11)	33
2.2.3.2.8 Procedure (PC200W Step 12)	33
Section 3. Overview	35
3.1 CR200(X) Overview	35
3.1.1 Programmed Instructions Are Evaluated Sequentially	36
3.1.2 Sensor Support	37
3.1.3 Input / Output Interface: The Wiring Panel	37
3.1.3.1 Measurement Inputs	37
3.1.3.2 Voltage Outputs	39
3.1.3.3 Grounding Terminals	39
3.1.3.4 Power Terminals	40
3.1.3.5 Communications Ports	40
3.1.4 Power Requirements	41
3.1.5 Programming: Firmware and User Programs	41
3.1.5.1 Firmware: OS and Settings	42
3.1.5.2 User Programming	42
3.1.6 Memory and Data Storage	42
3.1.7 Communications Overview	43
3.1.7.1 PakBus	43
3.1.7.2 Modbus	44
3.1.8 Maintenance Overview	44
3.1.8.1 Protection from Water	44
3.1.8.2 Protection from Voltage Transients	45
3.1.8.3 Calibration	45
3.1.8.4 Replacing the Internal Battery	45
3.2 PC Support Software	46
3.3 Specifications	47
Section 4. Sensor Support	49
4.1 Powering Sensors	49
4.1.1 Switched Precision	49
4.1.2 Continuous Unregulated (Nominal 12 Volt)	49
4.1.3 Switched Unregulated (Nominal 12 Volt)	50
4.2 Voltage Measurement	50
4.2.1 Measurement Sequence	50
4.2.2 Measurement Accuracy	50
4.2.3 Voltage Range	52
4.2.4 Integration	52
4.2.5 Self-Calibration	53
4.3 Bridge Resistance Measurements	53
4.3.1 Measurements Requiring AC Excitation	54
4.4 Pulse Count Measurement	54
4.4.1 Pulse input Channels	55
4.4.1.1 Pulse Input (P_SW)	56
4.4.1.2 Low-Level AC (P_LL)	57
4.4.2 Pulse Input on Digital I/O Channels C1–C2	57
4.5 Period Averaging Measurements	57
4.6 SDI-12 Recording	58
4.7 Cabling Effects on Measurements	58
4.7.1 Analog Sensor Cables	58
4.7.2 Pulse Sensors	58
4.7.3 Serial Sensors	59
4.7.3.1 SDI-12 Sensors	59
Section 5. Measurement and Control Peripherals	61
5.1 Control Output	61
5.1.1 Binary Control	61
5.1.1.1 Digital I/O Ports	61
5.1.1.2 Switched 12 V Control	62
5.1.1.3 Relays and Relay Drivers	62
5.1.1.4 Component Built Relays	62
5.2 Other Peripherals	63
5.2.1 TIMs	63
Section 6. CR200(X) Power Supply	65
6.1 Power Requirement	65
6.2 Calculating Power Consumption	65
6.3 Power Supplies	65
6.3.1 Battery Connection	65
Section 7. Grounding	67
7.1 ESD Protection	67
7.1.1 Lightning Protection	68
7.2 Single-Ended Measurement Reference	69
Section 8. CR200(X) Configuration	71
8.1 DevConfig	71
8.2 Sending the Operating System	72
8.2.1 Sending OS with DevConfig	72
8.3 Settings	74
8.3.1 Settings via DevConfig	74
8.3.1.1 Deployment Tab	76
8.3.1.2 Logger Control Tab	77
8.3.2 Settings via CRBASIC	78
8.3.3 Settings via Terminal Emulator	78
8.3.4 Durable Settings	79
Section 9. Programming	81
9.1 Inserting Comments into Program	81
9.2 Sending Programs	81
9.3 Writing Programs	81
9.3.1 Short Cut Editor and Program Generator	82
9.3.2 CRBASIC Editor	82
9.4 Numerical Formats	83
9.5 Structure	84
9.6 Declarations I - Single-line Declarations	85
9.6.1 Variables	85
9.6.1.1 Arrays	86
9.6.1.2 Dimensions	87
9.6.1.3 Data Types	87
9.6.1.4 Flags	87
9.6.2 Constants	88
9.6.2.1 Predefined Constants	88
9.6.3 Alias and Unit Declarations	89
9.7 Declarations II - Declared Sequences	89
9.7.1 Data Tables	89
9.7.1.1 DataTable () and EndTable () Instructions	92
9.7.1.2 DataInterval () Instruction	93
9.7.1.3 Output Processing Instructions	93
9.7.2 Subroutines	95
9.8 Program Execution Timing	95
9.9 Instructions	96
9.9.1 Measurement and Data Storage Processing	96
9.9.2 Parameter Types	97
9.9.3 Names in Parameters	97
9.9.4 Expressions in Parameters	98
9.9.5 Arrays of Multipliers and Offsets	98
9.10 Expressions	99
9.10.1 Floating Point Arithmetic	99
9.10.2 Mathematical Operations	99
9.10.3 Logical Expressions	100
9.11 Program Access to Data Tables	102
Section 10. CRBASIC Programming Instructions	105
10.1 Program Declarations	105
10.1.1 Variable Declarations & Modifiers	105
10.1.2 Constant Declarations	105
10.2 Data Table Declarations	106
10.2.1 Data Table Modifiers	106
10.2.2 Data Storage Output Processing	106
10.2.2.1 Single-Source	106
10.2.2.2 Multiple-Source	107
10.3 Single Execution at Compile	107
10.4 Program Control Instructions	108
10.4.1 Common Controls	108
10.5 Measurement Instructions	110
10.5.1 Diagnostics	110
10.5.2 Voltage	110
10.5.3 Pulse	110
10.5.4 Digital I/O	111
10.5.5 SDI-12	111
10.6 Processing and Math Instructions	112
10.6.1 Mathematical Operators	112
10.6.2 Logical Operators	112
10.6.3 Trigonometric Functions	113
10.6.3.1 Derived Functions	113
10.6.3.2 Intrinsic Functions	113
10.6.4 Arithmetic Functions	114
10.6.5 Spatial Processing	115
10.6.6 Other Functions	116
10.7 Clock Functions	116
10.8 Serial Input / Output	117
10.9 Peer-to-Peer PakBus Communications	117
10.10 Data Table Access and Management	118
10.11 SCADA	119
10.12 Satellite Systems Programming	120
10.12.1 GOES	120
Section 11. Programming Resource Library	121
11.1 Remote Sensor Interface	121
11.2 Radio Power Minimization	122
11.3 Multiple Switch Closure Measurements	124
11.4 SDI-12 Sensor Support	124
11.4.1 SDI-12 Command Basics	124
11.4.1.1 Addressing	126
11.4.1.1.1 Address Query Command (?!)	126
11.4.1.1.2 Change Address Command (aAb!)	126
11.4.1.1.3 Send Identification Command (aI!)	126
11.4.1.2 Start Measurement Commands (aM! & aC!)	126
11.4.1.2.1 Start Measurement Command (aMv!)	127
11.4.1.2.2 Start Concurrent Measurement Command (aC!)	127
11.4.1.2.3 Aborting a Measurement Command	127
11.4.1.3 Send Data Commands (aDv! & aRv!)	127
11.4.1.3.1 Send Data Command (aDv!)	127
11.4.1.3.2 Continuous Measurements Command (aRv!)	128
11.4.2 SDI-12 Communications	128
11.4.2.1 SDI-12 Transparent Mode	128
11.4.2.2 SDI-12 Programmed Mode	129
11.4.3 SDI-12 Power Considerations	130
11.5 Wind Vector	132
11.5.1 OutputOpt Parameters	132
11.5.2 Wind Vector Processing	132
11.5.2.1 Measured Raw Data	133
11.5.2.2 Calculations	133
11.5.2.2.1 Input Sample Vectors	133
11.5.2.2.2 Mean Wind Vector	135
11.6 TrigVar and DisableVar - Controlling Data Output and Output Processing	137
11.7 Multiple Data Intervals in Data Tables	138
Section 12. Memory and Data Storage	141
12.1 Data Storage	141
12.1.1 Data Table Storage	141
12.2 Memory Conservation	142
12.3 Memory Reset	142
12.3.1 Full Memory Reset	142
12.3.2 Program Send Reset	142
12.3.3 Manual Data Table Reset	142
Section 13. Telecommunications and Data Retrieval	143
13.1 Hardware and Carrier Signal	143
13.2 Protocols	144
13.3 Initiating Telecommunications	144
13.4 Data Retrieval	144
13.4.1 Via Telecommunications	144
13.4.2 Data Format on Computer	144
Section 14. PakBus Overview	145
14.1 PakBus Addresses	145
14.2 Nodes: Leaf Nodes and Routers	145
14.3 Router and Leaf Node Configuration	146
14.4 Linking Nodes: Neighbor Discovery	146
14.4.1 Hello-message (two-way exchange)	147
14.4.2 Beacon (one-way broadcast)	147
14.4.3 Hello-request (one-way broadcast)	147
14.4.4 Neighbor Lists	147
14.4.5 Adjusting Links	147
14.4.6 Maintaining Links	148
14.5 Troubleshooting	148
14.5.1 Link Integrity	148
14.5.1.1 Automatic Packet Size Adjustment	149
14.5.2 Ping	149
14.5.3 Traffic Flow	150
14.6 LoggerNet Device Map Configuration	150
Section 15. Alternate Telecoms Resource Library	151
15.1 Modbus	151
15.1.1 Overview	151
15.1.2 Terminology	151
15.1.2.1 Glossary of Terms	152
15.1.3 Programming for Modbus	152
15.1.3.1 Declarations	152
15.1.3.2 CRBASIC Instructions - Modbus	153
15.1.3.3 Addressing (ModbusAddr)	153
15.1.3.4 Supported Function Codes (Function)	153
15.1.3.5 Reading Inverse Format Registers	154
15.1.4 Troubleshooting	154
Section 16. Support Software	155
16.1 Short Cut	155
16.2 PC200W	155
16.3 Visual Weather	155
16.4 PC400	156
16.5 RTDAQ	156
16.6 LoggerNet Suite	156
16.7 PDA Software	157
16.8 Network Planner	157
Section 17. Care and Maintenance	159
17.1 Temperature Range	159
17.2 Moisture Protection	159
17.3 Enclosures	159
17.4 Replacing the Internal Battery	160
Section 18. Troubleshooting	163
18.1 Programming	163
18.1.1.1 Status Table as Debug Resource	163
18.1.1.2 SkippedScan	163
18.1.1.3 VarOutOfBounds	163
18.1.1.4 WatchdogErrors	163
18.1.1.5 TrapCode	164
18.1.1.6 Compile and Download Errors	164
18.1.2 NAN and ±INF	165
18.1.2.1 Measurements and NAN	165
18.1.2.1.1 Voltage Measurements	165
18.1.2.1.2 SDI-12 Measurements	165
18.1.2.2 Floating Point Math, NAN, and ±INF	165
18.2 Communications	166
18.2.1 RS-232	166
18.2.2 Communicating with Multiple PC Programs	166
18.3 Power Supply	167
18.3.1 Overview	167
18.3.2 Troubleshooting at a Glance	167
18.3.3 Diagnosis and Fix Procedures	168
18.3.3.1 Battery Voltage Test	168
18.3.3.2 Charging Circuit Test - Solar Panel	169
18.3.3.3 Charging Circuit Test - Transformer	170
18.3.3.4 Adjusting Charging Circuit Voltage	171
Appendix A. Glossary	173
A.1 Terms	173
A.2 Concepts	185
A.2.1 Accuracy, Precision, and Resolution	185
Appendix B. Status Table and Settings	187
Appendix C. Serial Port Pin Outs	193
C.1 RS-232 Communications Port	193
C.1.1 Pin-Out	193
Appendix D. ASCII / ANSI Table	195
Appendix E. Antenna Usage and Compliance	199
E.1 Use of Antenna with CR200(X)	199
E.2 Part 15 FCC Compliance Warning	199
E.2.1 Use of Approved Antennas	200
Index	201