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3... I
NTERFACE
M
ODULES
U
SING THE
OMP-MODL
3-41
additive lead wire resistance can be ignored (eg in thermistor or Kohm resistance
measurements). However, in applications of RTDs or lower resistance ranges this
lead wire resistance can add up to substantial measurement errors... especially if
long runs or lighter gauge lead wire is used. For example, in a 100 ohm RTD, 0.4
ohms of lead wire resistance would translates to a reading error of 1 Deg C.
To minimize these lead wire induced errors, the MLIM-4 supports 3-wire and 4-wire
connection methods. Connection diagrams and descriptions for each of the wiring
methods follow.
2-Wire Configuration
The 2-wire configuration is easiest to use and allows for utilization of all four
input channels of the MLIM-4 as individual channels. All three input types,
RTD, thermistor, and resistance can be measured with the 2-wire technique.
For short runs, heavier gauge lead wires and/or higher resistance
measurements, the 2-wire technique will provide excellent performance with
minimal error.
Calculating Lead Wire Effects
To calculate resistance errors induced by lead wires in a 2-wire
configuration:
1. Estimate the total length of the lead wire to be used.
2. Multiply this length by the resistance per foot of the wire
to be used. Complete wire tables are available from wire
manufacturers and in many electronic reference books.
For general reference, an abbreviated table is included
below.
Note that wire resistances are typically given per 1000
foot.
3. Assess the effects of this resistance on the required
accuracy. For RTD applications, tables are available
from the manufacturer that correlate RTD element
resistance to degrees over the usable range. As a
general guideline, a 100 ohm RTD will have a 1 Degree
C change for every 0.36 ohms, a 1000 ohm RTD will
have a 1 degree C change for every 3.6 ohms (hence the
increasing popularity of the 1000 ohm RTD).
Wire Gauge
ohms per 1000 ft
@ 25C (77F)
ohms per 1000 ft
@ 65C (149F)
26
41.6
48
24
26.2
30.2
22
16.5
19.0
20
10.4
11.9
18
6.5
7.5
16
4.1
4.7
Table 5: Typical Copper Wire resistance
2-Wire
Config
Summary of Contents for OMP-MODL
Page 1: ......
Page 9: ...1 INTRODUCTION USING THE MODULOGGER 1 7 13 ...
Page 23: ...2 OMP MODL System Base Using the OMP MODL 2 14 NOTES ...
Page 24: ...2 ModuLogger System Base Using the ModuLogger 2 1 ...
Page 30: ...3 INTERFACE MODULES USING THE OMP MODL 3 6 NOTES ...
Page 70: ...3 INTERFACE MODULES USING THE OMP MODL 3 46 NOTES ...
Page 76: ...3 INTERFACE MODULES USING THE OMP MODL 3 52 NOTES ...
Page 82: ...3 INTERFACE MODULES USING THE OMP MODL 3 58 NOTES ...
Page 83: ...3 INTERFACE MODULES USING THE MODULOGGER 3 1 ...
Page 105: ...5 HYPERCOMM COMMUNICATIONS USING THE OMP MODL 5 18 NOTES ...
Page 106: ...5 HYPERCOMM COMMUNICATIONS USING THE MODULOGGER 5 1 ...
Page 117: ...6 PCMCIA CARD CONFIGURATION AND USE USING THE MODULOGGER 6 1 ...
Page 134: ...7 HYPERNET ICON BASED PROGRAMMING USING THE OMP MODL 7 17 NOTES ...
Page 141: ...8 P P C D U OMP MODL ...
Page 149: ...9 HYPERPLOT GRAPHIC DATA DISPLAY USING THE OMP MODL 9 8 ...
Page 161: ...10 HYPERTRACK REAL TIME DATA DISPLAY USING THE OMP MODL 10 12 NOTES ...
Page 162: ...10 HYPERTRACK REAL TIME DATA DISPLAY USING THE OMP MODL 10 1 ...
Page 163: ...11 APPENDICES USING THE OMP MODL 11 1 11 APPENDICES ...
Page 164: ...11 APPENDICES USING THE OMP MODL 11 2 NOTES ...
Page 270: ...11 APPENDIX A MASTER ICON FILE REFERENCE USING THE OMP MODL 11 108 ...
Page 276: ...11 APPENDIX C HYPERWARE FILE LISTING USING THE OMP MODL 11 114 NOTES ...
Page 278: ...11 APPENDIX C HYPERWARE FILE LISTING USING THE OMP MODL 11 116 NOTES ...
Page 279: ......
Page 282: ...11 APPENDIX E CHANGING THE OMP MODL EPROM USING THE OMP MODL 11 120 NOTES ...
Page 288: ...11 APPENDIX G HYPERNET THEORY OF OPERATION USING THE OMP MODL 11 126 NOTES ...
Page 290: ...11 APPENDIX I RS 232 CABLE PORT AND ADAPTER USING THE OMP MODL 11 128 NOTES ...
Page 297: ...11 APPENDIX K MODEM CONFIGURATION USING THE OMP MODL 11 135 ...