Keithley’s 5½-digit Model 6517B Electrometer/High Resistance Meter offers accuracy and sensitivity specifications unmatched by any other meter of this type. It also offers a variety of features that simplify measuring high resistances and the resistivity of insulating materials. With reading rates of up to 425 read ings/second, the Model 6517B is also significantly faster than competitive electrometers, so it offers a quick, easy way to measure low-level currents.
Exceptional Performance Specifications
The half-rack-sized Model 6517B has a special low current input amplifier with an input bias current of <3fA with just 0.75fA p-p (peak-to-peak) noise and <20µV burden voltage on the lowest range. The input impedance for voltage and resistance measurements is 200TΩ for near-ideal circuit loading. These specifications ensure the accuracy and sensitivity needed for accurate low current and high imped ance volt age, resistance, and charge measure ments in areas of re search such as physics, optics, nanotechnology, and materials science. A built-in ±1kV voltage source with sweep capability simplifies performing leak age, break down, and resis tance testing, as well as volume (Ω-cm) and surface resistivity (Ω/square) mea sure ments on insulating materials.
Wide Measurement Ranges
The Model 6517B offers full autoranging over the full span of ranges on current, resistance, voltage, and charge mea sure ments:
- Current measurements from 1fA to 20mA
- Voltage measurements from 10µV to 200V
- Resistance measurements from 50Ω to 10 Ω
- Charge measurements from 10fC to 2µC
Improved High Resistivity Measurements
Many test applications require measuring high levels of resistivity (surface or volume) of materials. The conventional method of making these measurements is to apply a sufficiently large voltage to a sample, measure the current that flows through the sample, then calculate the resistance using Ohm’s Law (R=V/I). While high resistance materials and devices produce very small currents that are difficult to measure accurately, Keithley’s electrometers and picoammeters are used successfully for such measurements.
Even with high quality instrumentation, inherent background currents in the material can make these measurements difficult to perform accurately. Insulating materials, polymers, and plastics typically exhibit background currents due to piezoelectric effects, capacitive elements charged by static electricity, and polarization effects. These background currents are often equal to or greater than the current stimulated by the applied voltage. In these cases, the result is often unstable, providing inaccurate resistance or resistivity readings or even erroneous negative values. Keithley’s Model 6517B is designed to solve these problems and provides consistent, repeatable, and accurate measurements for a wide variety of materials and components, especially when used in combination with the Model 8009 Resistivity Test Fixture.
Alternating Polarity Method
The Model 6517B uses the Alternating Polarity method, which virtually eliminates the effect of any background currents in the sample. First and second order drifts of the background currents are also canceled out. The Alternating Polarity method applies a voltage of positive polarity, then the current is measured after a specified delay (Measure Time). Next, the polarity is reversed and the current measured again, using the same delay. This process is repeated continuously, and the resistance is calculated based on a weighted average of the four most recent current measurements. This method typically produces a highly repeatable, accurate measurement of resistance (or resistivity) by the seventh reversal on most materials (i.e., by discarding the first three readings). For example, a 1mm-thick sample of 10 14 Ω-cm material can be measured with 0.3% repeatability in the Model 8009 test fixture, provided the background current changes less than 200fA over a 15-second period.
Simple DMM-like Operation
The Model 6517B is designed for easy, DMM-like operation via the front panel, with single-button control of im por tant functions such as resistance measurement. It can also be controlled via a built-in IEEE-488 inter face, which makes it possible to program all func tions over the bus through a computer controller.
High Accuracy High Resistance Measurements
The Model 6517B offers a number of features and capabili ties that help ensure the accuracy of high resistance mea sure ment applications. For example, the built-in volt age source simplifies determining the relation ship between an insulator’s resistivity and the level of source voltage used. It is well suit ed for capacitor leakage and insulation resistance measurements, tests of the surface insula tion resistance of printed circuit boards, voltage coefficient test ing of resistors, and diode leakage characterization.
Temperature and Humidity Stamping
Humidity and temperature can influence the resist ivity values of materials significantly. To help you make accurate comparisons of readings acquired under varying conditions, the Model 6517B offers a built-in type K thermo couple and an optional Model 6517-RH Relative Humidity Probe. A built-in data storage buffer allows recording and recalling read ings stamped with the time, tempera ture, and relative humidity at which they were acquired.
Accessories Extend Measurement Capabilities
A variety of optional accessories can be used to extend the Model 6517B’s applications and enhance its performance.
Scanner Cards. Two scan ner cards are available to simplify scan ning multiple signals. Either card can be easily inserted in the option slot of the instru ment’s back panel. The Model 6521 Scan ner Card offers ten channels of low-level cur rent scanning. The Model 6522 Scanner Card provides ten channels of high impedance voltage switching or low current switching.
Test Fixture. The Model 8009 Resistivity Chamber is a guard ed test fixture for measuring volume and surface resistivities of sam ple materials. It has stain less-steel electrodes built to ASTM standards. The fixture’s electrode dimensions are pre- programmed into the Model 6517B, so there’s no need to calculate those values then enter them man ually. This accessory is designed to protect you from contact with potentially hazardous voltages —opening the lid of the cham ber automatically turns off the Model 6517B’s voltage source.
Applications
The Model 6517B is well suited for low current and high impedance voltage, resistance, and charge measurements in areas of re search such as physics, optics, and mater ials science. Its extremely low voltage bur den makes it particularly appropriate for use in solar cell applications, and its built-in voltage source and low current sensitivity make it an excellent solution for high resistance measurements of nano materials such as polymer based nanowires. Its high speed and ease of use also make it an excellent choice for quality control, product engineering, and production test appli ca tions involving leakage, breakdown, and resistance testing. Volume and sur face resistivity measurements on non-conduc tive mater ials are particularly enhanced by the Model 6517B’s voltage reversal method. The Model 6517B is also well suited for electro-chemistry applications such as ion selective electrode and pH measurements, conductivity cells, and potentiometry.
Model 6517B Enhancements
The Model 6517B is an updated version, replacing the earlier Model 6517A, which was introduced in 1996. Software applications created for the Model 6517A using SCPI commands can run without modi? cations on the Model 6517B. However, the Model 6517B does offer some useful enhancements to the earlier design. Its internal battery-backed memory buffer can now store up to 50,000 readings, allowing users to log test results for longer periods and to store more data associated with those readings. The new model also provides faster reading rates to the internal buffer (up to 425 readings/ second) and to external memory via the IEEE bus (up to 400 readings/ second). Several connector modifications have been incorporated to address modern connectivity and safety requirements.