Reliable High-Resistance Measurements Using the B2985A/87A

Introduction

Previously, high resistance and resistivity measurements have required extensive measurement expertise in order to obtain accurate results. This is primarily due to the nature of very low current measurements, which are extremely sensitive to a variety of environmental factors. Typical sources of error include leakage currents, discharge or absorption currents, test device grounding/floating issues, and environmental noise arising from the test device’s physical dimensions. 

The Keysight Electrometer/High Resistance Meter (B2985A/B2987A) provides both impressive 10 aA (0.01 fA) minimum current resolution and 10 PΩ (1016 Ω) resistance measurement capability. In addition, it provides many additional features to improve measurement confidence such as histogram and trend graph views and intuitive measurement navigation. 

The histogram and trend (Roll View) graph views provide a quick overview of the measurement status, allowing you to fix any test issues immediately. The measurement navigation aids help you to set up the correct measurement parameters even if you are a novice user. 

This application note explains how easy it is to make an accurate high resistance measurement using the B2985A/87A. 

Note: The B2987A has an internal rechargeable battery that allows it to operate without being connected to AC power.

Table of Content:

•  Keysight B2985A/87A Measurement Resources
• High Resistance Measurement Basics
• High Resistance Measurement Example
• High Resistance Test Accessories

Keysight B2985A/87A Measurement Resources 

By default, at boot-up, the measurement common (Common) of the ammeter and the voltmeter are connected to the low side of the voltage source (Vs Low). However, a simple command allows you to disconnect the Vs Low terminal from the circuit common using an internal switch (the Vs low terminal connection switch). This means that the voltage source (Vs) and the ammeter/ voltmeter resources can be used independently of one another. 

Floating device measurement 

The test device is connected between the Vs High output and the Ammeter input. Since the Ammeter measures very low currents and is very noise-sensitive, it is located close to the ground potential to shield the test device for better measurement results.

Grounded device measurement 

In this configuration, the Ammeter is connected to the Vs positive output because the device is grounded on one side.

Measurement support functionality and tips 

High-resistance measurements need to be performed for a wide variety of applications that include materials characterization, component tests, finished product evaluation, and even equipment maintenance. Unfortunately, many of these applications do not involve measuring a pure resistance because of the presence of parasitic components such as parallel capacitances, leakage resistances, and noise receptive antenna elements. Therefore, making accurate high-resistance measurements requires some expertise as to how to use the features of a measurement instrument to eliminate the influence of these parasitic elements. 

The following sections explain the techniques necessary to make accurate high resistance measurements.