SECTION 7. MEASUREMENT PROGRAMMING EXAMPLES
7-2
FIGURE 7.2-1. Typical Connection for Active Sensor with External Battery
7.2 DIFFERENTIAL VOLTAGE
MEASUREMENT
Some sensors either contain or require active
signal conditioning circuitry to provide an easily
measured analog voltage output. Generally, the
output is referenced to the sensor ground. The
associated current drain usually requires a
power source external to the CR10. A typical
connection scheme where AC power is not
available and both the CR10 and sensor are
powered by an external battery is shown in
Figure 7.2-1. Since a single-ended
measurement is referenced to the CR10 ground,
any voltage difference between the sensor
ground and CR10 ground becomes a
measurement error. A differential measurement
avoids this error by measuring the signal
between the 2 leads without reference to
ground. This example analyzes the potential
error on a water pH measurement using a
Martek Mark V water quality analyzer.
The wire used to supply power from the external
battery is 18 AWG with an average resistance of
6.5 ohms/1000 ft. The power leads to the CR10
and pH meter are 2 ft and 10 ft, respectively.
Typical current drain for the pH meter is 300 mA.
When making measurements, the CR10 draws
about 35 mA. Since voltage is equal to current
multiplied by resistance (V=IR), ground voltages
at the pH meter and the CR10 relative to battery
ground are:
pH meter ground =
0.3A x 10/1000 x 6.5ohms = +0.0195V
CR10 ground =
0.035A x 2/1000 x 6.5ohms = +0.0005V
Ground at the pH meter is 0.0190 V higher than
ground at the CR10. The meter output is 0-1
volt referenced to meter ground, for the full
range of 14 pH units, or 0.0714 V/pH. Thus, if
the output is measured with a single-ended
voltage measurement, it is 0.0190 V or 0.266
pH units too high. If this offset remained
constant, it could be corrected in programming.
However, it is better to use a differential voltage
measurement which does not rely on the
current drain remaining constant. The program
that follows illustrates the use of Instruction 2 to
make the measurement. A multiplier of 0.014 is
used to convert the millivolt output into pH
units.
PROGRAM
01:
P2
Volt (DIFF)
01:
1
Rep
02:
25
2500 mV 60 Hz rejection
03:
1
IN Chan
04:
1
Loc [:pH ]
05:
0.014
Mult
06:
0
Offset
Содержание CR10 PROM
Страница 2: ...This is a blank page ...
Страница 4: ...This is a blank page ...
Страница 9: ...CR10 TABLE OF CONTENTS v LIST OF TABLES LT 1 LIST OF FIGURES LF 1 INDEX I 1 ...
Страница 10: ...CR10 TABLE OF CONTENTS vi This is a blank page ...
Страница 14: ...CR10 OVERVIEW OV 2 ...
Страница 15: ...CR10 OVERVIEW OV 3 FIGURE OV1 1 1 CR10 and Wiring Panel ...
Страница 16: ...CR10 OVERVIEW OV 4 FIGURE OV1 1 2 CR10 Wiring Panel Instruction Access ...
Страница 17: ...CR10 OVERVIEW OV 5 ...
Страница 34: ...CR10 OVERVIEW OV 22 ...
Страница 35: ...CR10 OVERVIEW OV 23 FIGURE OV6 1 1 Data Retrieval Hardware Options ...
Страница 36: ...CR10 OVERVIEW OV 24 OV7 SPECIFICATIONS ...
Страница 37: ...CR10 OVERVIEW OV 25 ...
Страница 38: ...CR10 OVERVIEW OV 26 ...
Страница 51: ...SECTION 1 FUNCTIONAL MODES 1 13 This is a blank page ...
Страница 53: ...2 2 ...
Страница 62: ...SECTION 3 INSTRUCTION SET BASICS 3 6 ...
Страница 63: ...SECTION 3 INSTRUCTION SET BASICS 3 7 ...
Страница 68: ...SECTION 3 INSTRUCTION SET BASICS 3 12 This is a blank page ...
Страница 74: ...SECTION 4 EXTERNAL STORAGE PERIPHERALS 4 6 ...
Страница 79: ...SECTION 4 EXTERNAL STORAGE PERIPHERALS 4 11 10 0X X is current address enter address to change to 1 8 ...
Страница 88: ...6 5 FIGURE 6 6 1 Addressing Sequence for the RF Modem ...
Страница 110: ...SECTION 7 MEASUREMENT PROGRAMMING EXAMPLES 7 17 FIGURE 7 16 2 Well Monitoring Example ...
Страница 132: ...SECTION 8 PROCESSING AND PROGRAM CONTROL EXAMPLES 8 13 This is a blank page ...
Страница 197: ...SECTION 13 CR10 MEASUREMENTS 13 18 FIGURE 13 5 1 Circuits Used with Instructions 4 9 ...
Страница 203: ...SECTION 13 CR10 MEASUREMENTS 13 24 This is a blank page ...
Страница 215: ...SECTION 14 INSTALLATION AND MAINTENANCE 14 12 This is a blank page ...
Страница 218: ...APPENDIX A GLOSSARY A 3 and computers in a terminal mode fall in this category ...
Страница 220: ...APPENDIX A GLOSSARY A 5 This is a blank page ...
Страница 228: ...APPENDIX C BINARY TELECOMMUNICATIONS C 6 This is a blank page ...
Страница 230: ...This is a blank page ...
Страница 232: ...This is a blank page ...
Страница 234: ...APPENDIX G CHANGING RAM OR PROM CHIPS G 2 FIGURE G 1 Disassembling CR10 ...
Страница 235: ...APPENDIX G CHANGING RAM OR PROM CHIPS G 3 FIGURE G 2 Jumper Settings for Different RAM Configurations in Early CR10s ...
Страница 236: ...APPENDIX G CHANGING RAM OR PROM CHIPS G 4 FIGURE G 3 Jumper Settings and Locations ...
Страница 237: ...APPENDIX G CHANGING RAM OR PROM CHIPS G 5 This is a blank page ...
Страница 241: ...LIST OF TABLES LT 4 This is a blank page ...
Страница 253: ...CR10 INDEX I 10 This is a blank page ...