Low Level Measurements Handbook

More documents

Recommendations

Info

FIGURE 2-5: Guarded ConfigurationConnecting CableR SV SHICableShieldR LGUARDR G I GV M+A GUARD–LOVoltage SourceVoltmeter with Guard Bufferalso reduced, making the response speed of the circuit much faster. This isdiscussed in detail in the paragraphs on Shunt Capacitance Loading andGuarding.The source-measure unit (SMU) can also be used to measure voltagesfrom a high resistance source and the Guard terminal will make a similarimprovement.The circuit of the electrometer when used as a voltmeter is actually asshown in Figure 2-6. The guard amplifier is a unity-gain amplifier with veryhigh input impedance. The open-loop gain, A GUARD , ranges from 10 4 to 10 6 .The leakage resistance (R L ) is multiplied by this gain and the measured voltagebecomes:A GUARD RV LM = V S –––––––––––––––––( RS + A GUARD R L)Example: Assume R S has a value of 10GΩ and R L is 100GΩ. If we assumea mid-range value of 10 5 for A GUARD and a value of 10V for V S , the voltagemeasured by the meter is:10V 16M = 10 ––––––––––––––––––V M = 9.99999V( 1.000001 × 1016 )Thus, we see the loading error with guarding is less than 0.001%. Incontrast, the unguarded error voltage with this combination of source andshunt resistances would be about 9%.Shunt Capacitance Loading and GuardingThe settling time of a voltage measurement depends both on the equivalentsource resistance and the effective capacitance at the input of the voltmeter;<strong>Measurements</strong> from High Resistance Sources 2-7
FIGURE 2-6: Guarding Leakage ResistanceHI+R SR LV MA GUARD–GUARDV SLOVoltage SourceVoltmeter with Guard BufferA GUARD = 10 4 to 10 6V M = V SA GUARD R LR S + A GUARD R LFIGURE 2-7: Shunt Capacitance LoadingHIQ INR SV SShuntCapacitanceC SHUNTV MLOVoltage SourceVoltmeterV M = V S (1 – e –t/R SC SHUNT )Q IN = V S C SHUNT2-8 SECTION 2
Page 1 and 2: www.keithley.comLLM6 th EditionLow
Page 4 and 5: TABLE OF C ONTENTSSECTION 1 Low Lev
Page 6 and 7: 3.3 Low Resistance Measurements....
Page 8 and 9: SECTION 1Low Level DCMeasuringInstr
Page 10 and 11: 1.1 IntroductionDC voltage, DC curr
Page 12 and 13: FIGURE 1-3: Typical Digital Multime
Page 14 and 15: Coulombmeter FunctionCurrent integr
Page 16 and 17: 1.3.6 The SourceMeter ® Instrument
Page 18 and 19: TABLE 1-1: Specification Conversion
Page 20 and 21: Transfer StabilityA special case of
Page 22 and 23: FIGURE 1-6: Common Mode NoiseMeasur
Page 24 and 25: FIGURE 1-8: Voltage Amplifier+-V 2A
Page 26 and 27: Picoammeter amplifier gain can be c
Page 28 and 29: Using a small-signal transistor in
Page 30 and 31: FIGURE 1-17: High Resistance Measur
Page 32 and 33: FIGURE 1-20: High Resistance Measur
Page 34 and 35: Micro-ohmmeterThe micro-ohmmeter al
Page 36 and 37: FIGURE 1-26: Typical Digital Electr
Page 38 and 39: In order to cancel internal offsets
Page 40: Sense circuitry is used to monitor
Page 43 and 44: 2.1 IntroductionAs described in Sec
Page 45 and 46: cause significant loading errors. I
Page 47: Cable leakage resistance is a commo
Page 51 and 52: Example: Assume R S = 10GΩ and C S
Page 53 and 54: MaterialTABLE 2-2: Properties of Va
Page 55 and 56: QuartzQuartz has properties similar
Page 57 and 58: FIGURE 2-11: Guarding as Applied to
Page 59 and 60: FIGURE 2-13: Guarding the Leakage R
Page 61 and 62: FIGURE 2-15: Simplified Model of a
Page 63 and 64: time and/or temperature. Zero offse
Page 65 and 66: open-circuited, allow the reading t
Page 67 and 68: to equalize charges and minimize ch
Page 69 and 70: If insulators become contaminated,
Page 71 and 72: The input resistance of a feedback
Page 73 and 74: ence. However, in some cases, shiel
Page 75 and 76: FIGURE 2-27: Feedback Coulombmeter
Page 77 and 78: Advantages of Using a Coulombmeter
Page 79 and 80: FIGURE 2-30: Constant-Voltage Metho
Page 81 and 82: In addition to the voltage drop lim
Page 83 and 84: FIGURE 2-34a: Effects of Cable Resi
Page 85 and 86: Such devices require extreme care i
Page 87 and 88: charge will be lost through the zer
Page 89 and 90: FIGURE 2-40: Proper ConnectionCurre
Page 91 and 92: Figure 2-43 shows an example of AC
Page 93 and 94: fering voltage or current. A guard
Page 95 and 96: esponse is the rise time of the ins
Page 97 and 98: FIGURE 2-47: Shunt Capacitance Effe
Page 99 and 100:
Resistance Measurements (Constant-C
Page 101 and 102:
FIGURE 2-52: Noise Voltage vs. Band
Page 103 and 104:
Source ResistanceAfter the bandwidt
Page 105 and 106:
a. ConfigurationShieldCenterconduct
Page 107 and 108:
• Shielding and Guarding: The fix
Page 109 and 110:
floating circuits, a second grounde
Page 111 and 112:
3.1 IntroductionLow voltage and low
Page 113 and 114:
Thermoelectric EMFsThermoelectric v
Page 115 and 116:
Reversing Sources to Cancel Thermoe
Page 117 and 118:
quency spectrum of these interferen
Page 119 and 120:
ment is almost entirely determined
Page 121 and 122:
FIGURE 3-9: Low Voltages Generated
Page 123 and 124:
FIGURE 3-11a: Multiple Grounds (Gro
Page 125 and 126:
Common-Mode Reversal ErrorsReversin
Page 127 and 128:
FIGURE 3-14: Two-Wire Resistance Me
Page 129 and 130:
FIGURE 3-16: Canceling Thermoelectr
Page 131 and 132:
Both V A and V B are affected by th
Page 133 and 134:
If using a micro-ohmmeter or DMM to
Page 135 and 136:
FIGURE 3-20: Dry Circuit Testing Us
Page 137 and 138:
SECTION 4Applications
Page 139 and 140:
For timing and integrating applicat
Page 141 and 142:
FIGURE 4-2:Using an Electrometer to
Page 143 and 144:
If current flows, the electrodes wi
Page 145 and 146:
4.3 Low Current Measurement Applica
Page 147 and 148:
DC. The Model 6517A can also be use
Page 149 and 150:
voltage (V DS ) and measures the re
Page 151 and 152:
The Keithley Model 248 High Voltage
Page 153 and 154:
FIGURE 4-16: Ion Collector with Gro
Page 155 and 156:
Figure 4-19 shows a Model 6430 conn
Page 157 and 158:
FIGURE 4-21: SIR Test System to Mea
Page 159 and 160:
FIGURE 4-22: Volume ResistivityElec
Page 161 and 162:
these problems, the Alternating Pol
Page 163 and 164:
FIGURE 4-25: Four-Point Collinear P
Page 165 and 166:
Using two electrometers eliminates
Page 167 and 168:
A plot of this function is shown in
Page 169 and 170:
FIGURE 4-31: van der Pauw Measureme
Page 171 and 172:
Through interactive programming, th
Page 173 and 174:
objects. As discussed in Section 2.
Page 175 and 176:
FIGURE 4-36: Faraday CupOutside Ele
Page 177 and 178:
FIGURE 4-38: Connections for Standa
Page 179 and 180:
FIGURE 4-40: Microcalorimeter with
Page 181 and 182:
Measurement MethodFigure 4-42 illus
Page 183 and 184:
FIGURE 4-43: Using a Nanovoltmeter
Page 185 and 186:
exceed the critical current of the
Page 187 and 188:
equation for V/I. Most materials ha
Page 189 and 190:
FIGURE 4-49: van der Pauw Connectio
Page 191 and 192:
5.1 IntroductionChoosing a specific
Page 193 and 194:
TABLE 5-1a: Low Current/High Resist
Page 195 and 196:
Table 5-1b: Source-Measure Instrume
Page 197 and 198:
Table 5-2: High Speed Power Supplie
Page 199 and 200:
Table 5-3: Connectors, Adapters, an
Page 201 and 202:
Table 5-4: CablesTERMINATIONS LENGT
Page 203 and 204:
Table 5-5: Test Leads and ProbesMOD
Page 205 and 206:
Table 5-6: Switching Cards for the
Page 207 and 208:
Page 209 and 210:
Page 211 and 212:
APPENDIX ALow LevelMeasurementTroub
Page 213 and 214:
Measurement Type andTypical Applica
Page 215 and 216:
Proper cable and connector assembly
Page 217 and 218:
APPENDIX CGlossary
Page 219 and 220:
channels. For matrix cards, a chann
Page 221 and 222:
R. Buckminster Fuller. Sometimes ca
Page 223 and 224:
NORMAL-MODE REJECTION RATIO (NMRR).
Page 225 and 226:
SOURCEMETER. A SourceMeter instrume
Page 227 and 228:
APPENDIX DSafetyConsiderations
Page 229 and 230:
The types of product users are:Resp
Page 231 and 232:
are the same. Other components that
Page 233 and 234:
1/f noise, 3-7 to 3-83dB point, 2-5
Page 235 and 236:
Normal mode rejection ratio (NMRR),
Page 237 and 238:
Specifications are subject to chang
Page 239:
Specifications are subject to chang
show all

Low Level Measurements Handbook

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?