Customers are no longer left with having to use substitution method provided by Teraohmeter type devices for simulated results. Actual ratio bridge measurements are now achievable with the all new 6600A and 6650A from Measurements International.

The model 6600A is a low cost Dual Source High Resistance Meter using the preferred ‘Dual Source’ method for measuring high resistance in the range of 100 kΩ to 10 PΩ.

The simplified construction and operation of the 6600A offers much improved operation and performance over the typical teraohmmeter/electrometer, with a more user friendly approach to high resistance measurements. The 6600A has numerous advantages over single input devices like the typical teraohmmeter/electrometer such as reliability, trace ability and the fact that measurements are not dependent on short term stability or repeatability of the measurement circuit.

Technology

Since the mid 1990’s the modified Wheatstone bridge or Dual Source resistance bridge has set the standard for high precision measurement of resistances from 109 to 1014. Over the years, this technology has been further developed to the point that it has replaced all other technologies by utilizing a true “Bridge” measurement circuit, the Unit Under Test (UUT) is compared to a working or primary standard to produce a “Live Ratio”.  The 6600A and 6650A are the only “bridges” commercially available for high resistance measurements. Any value resistor up to and including the 1016Ω level can be measured at ratios up to 100:1.  Menu driven functions are selectable using the menu displayed for calibration, ratio measurements and absolute measurements. For the absolute measurements the value and related uncertainty of the reference resistor are entered. Measurement functions such as voltage across the unknown resistor and settle time, number of measurements and number of statistics are all also entered. The user has the option to display data (several measurements at a time), a combination of data and a graph of the measurements or just the graph. All uncertainty calculations are 2 sigma calculations.

In Figure 3 Measurements International Has further modified the  Wheatstone bridge/DSB to include two stable Voltage Sources with IEEE488 in place of the two resistors R1 and R2. Instead of adjusting R1 in the Wheatstone bridge, the DSB is balanced by adjusting one or both voltage sources and at zero balance on the detector the ratio of the voltage sources is equal to the ratio of resistances (equation 3). The DSB has the advantage that the unwanted capacitances and resistances associated to R1 and R2 in the Wheatstone bridge are lessened due to the low output impedances of the voltage sources.

Versatility

The 6600A are enabled with numerous measurement functions that allow users to tailor their measurements for their own particular needs.

Live Ratio Mode

The most accurate mode of use is the live ratio mode where the Bridge architecture is formed by substituting two of the resistive arms of a Wheatstone bridge circuit with low-impedance digitally-programmable voltage sources. In this mode a UUT is compared to a standard reference Measurements International is the only manufacturer of High resistance measurement systems whose measurement capabilities support its product specifications. resistor providing a live ratio to the reference resistor. Measurements in this mode can further be improved by utilizing a resistor substitution method and thus removing the uncertainty contributor of the bridge.

Direct Measurement Mode

In this mode, the UUT is measured directly. This mode offers the same functionality that is utilized on a less accurate single input device such as the teraohmmeter. The 6600A offers users the ability to quickly establish nominal values, measure Insulation Resistance, Volume and Surface resistivity. This mode is also useful for determining resistor time constants, as well as voltage and temperature coefficients.

Voltage and Current Measurements

Voltage and Current Measurements – Service mode features the ability to measure voltages from 1V to 1100V DC and currents from 10-5 to 10-15 Amps.

Voltage Range

The 1000 V DC sources offer voltage ratios of 1, 10, 100, and 1000 or any ratio in between. The voltage settings can be observed on the front panel display. The model 6600A are the only commercially available High Resistance Bridges which offers any selectable voltage between 1 V to 1000 V. Other manufacturers are limited to specific voltages within the set range of 1 V to 1000 V.

Front Panel Operation

The front panel offers users simple and intuitive measurement options. Features include resistor protection, settle time to verify time constants of resistors, number of measurements, statistics, voltage and temperature coefficients and graphing.  Users can create and combine several program tasks such as inter-comparing standards to standards, standards to measurands, and measurands to measurands. Selectable parameters include measurement time delays (wait times), settle time, number of measurement, applied voltage, number of runs, standards used, reversal rate, current threshold, and standard resistor uncertainty. All measurement parameters including statistical data are displayed during measurement.

Software

Making a measurement on the 6650A is simple. Software allows the user to define the measurement and test parameters utilizing the same proven software used on the MI 6010 and 6000 series of DC Bridges that our customers have become accustomed to. Features include resistor protection, settle time to verify time constants of resistors, number of measurements, statistics, voltage and temperature coefficients and graphing. Programs Menu allows users to create and combine several program tasks such as inter-comparing standards to standards, standards to measurands and measurands to measurands. Selectable parameters include measurement time delays (wait times), settle time, number of measurement, applied voltage, number of runs, standards used, reversal rate, current threshold, and standard resistor uncertainty. All measurement parameters including statistical data is displayed during measurement.

Accuracy/Uncertainty

The 6600A provides the Best Accuracy and Uncertainty Commercially available today! Other manufacturers can claim various levels of accuracy and uncertainty, but we ask you to verify these claims through your National Laboratory, or if you are the National Laboratory, please verify through any Major NMI as to what they are using to measure High Resistance! Measurements International is the only manufacturer of High resistance measurement systems whose measurement capabilities support its product specifications.

Complete Automation

Metrologists currently are met with an increased workload which can be greatly reduced with the automation features of the 6600A High Resistance Systems. With the incorporation of the new 4610A and 4620A High Resistance scanners, Metrologists now have the ability to fully automate the full measurement range! Simply setup your program, start your measurement, and only come back when the run is completed to gather your data.

Calibration of the model 6600A requires only the use of an 8.5 Digit DVM for traceability. Optionally, the bridge may be characterized at any time by employing a resistor interchange as described in the operator manual.