Characterisation, Measurement & Analysis
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SRS SR715 LCR Meter

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Product Code: 14944
Manufacturer: Stanford Research Systems

  • 0.05% basic accuracy (SR720), 0.2% (SR715)

  • Five digit display of L, C, R and Q or D

  • Test frequencies to 100 kHz

  • Up to 20 measurements per second

  • Binning and limits for part sorting

  • Standard RS-232 interface

  • External capacitor bias up to 40 V

  • Optional GPIB and handler interface

The Stanford Research Systems SR715 & SR720 family of LCR Meters quickly and accurately measures passive components with as little as 0.05% error. These easy-to-use instruments are simple to set up, adjust and calibrate. These factors, combined with low cost, make these meters perfect for applications such as incoming inspection, quality control, automated test, and general bench top use.

Five different test frequencies, three preset voltage levels, internal and external capacitor biasing, and three different measurement speeds allow unmatched flexibility to create your own test environment. The convenient auto measure mode simplifies measuring unknown parts by automatically calculating the best part model and range for any component.

Stray impedances are removed from measurements with a simple, fast, null calibration procedure. The built-in Kelvin fixture handles radial lead components, and adapters are included for axial components. Optional fixtures include SMD tweezers, Kelvin clips, and BNC adapters.

Built-in binning sorts your components into overlapping or sequential bins. Up to nine complete instrument configurations may be saved to non-volatile memory for quick set up. For easy integration with computerized test environments an RS-232 interface is standard, IEEE-488 and handler interfaces are optional.

Simple to Operate
The power and flexibility of the SR715/720 does not come at the expense of ease of use. A convenient AUTO measurement mode automates the selection of setup parameters and quickly determines the appropriate device model for whatever component is being measured. Auto Range automatically selects the appropriate units and display resolution for the DUT. And up to 9 complete instrument setups can be stored in non-volatile memory for quick recall at a later time.

The SR715/720's Kelvin fixture uses two wires to carry the test current and two independent wires to sense the voltage across the device under test (DUT). This prevents the voltage drop in the current carrying wires from affecting the voltage measurement. Radial leaded components are simply inserted into the test fixture, one lead in each side. Axial leaded devices require the use of the standard axial fixture adapters. Surface mount (SMD) devices or components with large or unusually shaped leads can be measured with SMD tweezers or Kelvin clips. The tweezers and clips attach directly to the SR715/720 test fixture. An optional BNC fixture adapter allows you to connect a remote fixture or other equipment through one meter of coaxial cable.

The five digit LED display shows measured values, entered parameters, instrument status, and user messages. When making normal measurements, the major parameter (L, C, or R) is shown on the left display and the appropriate minor parameter (Q, D or R) is shown on the right display (see the following SRS Tech Note for a discussion of these parameters). The number of displayed digits and the location of the decimal points are automatically adjusted according to the selected range and resolution. Indicator LEDs show the parameter (L, C, or R and Q, D, or R) being displayed. Measurements can be displayed as nominal values, deviations, or as percentage deviation. Units of the major parameter (Ohms, Farads, or Henrys) are indicated by LEDs located between the two displays. The minor parameter is either dimensionless (Q and D) or has the units of Ohms (R). Status information relating to the remote interfaces is conveniently displayed on the front panel.

Parameter Selection
Measurements can be performed at a number of discrete frequencies: 100 Hz, 120 Hz, 1 kHz, 10 kHz or 100 kHz (SR720 only). The drive voltage can be selected to preset values (0.1, 0.25 and 1.0 V), or set from 0.0 to 1.0 V in 50 mV increments. Both series or parallel equivalent circuit models of a component can be measured. Capacitor measurements use either the internal 2.0 VDC bias or an external DC source of up to 40 V. External bias is applied through the back panel banana jacks, and is fused at 250 mA.

Either continuous or triggered measurements can be selected. Measurements are triggered from the front panel, through the optional handler interface, or through either computer interface. Measurements can be taken at rates of 2, 10, or 20 measurements per second for test frequencies of 1 kHz or higher. Consecutive readings can be averaged between 2 and 10 times for increased accuracy.

The SR715/720 has built-in features to aid in component sorting. This is especially useful for production testing, incoming inspection, device matching or when you need to test multiple devices of similar value. The binning feature simplifies parts sorting by eliminating the need to read the major and minor parameters and then deciding what to do with each part. Binning configurations can be entered from the keyboard or over any of the computer interfaces. The SR715/7220 allows you to sort components into as many as ten different bins. The meters support three types of binning schemes: pass/fail, overlapping and sequential. Pass/Fail has only two bins; good parts and everything else. Overlapping (or nested) bins have one nominal value and are sorted into progressively larger bins (i.e., ±1%, ±2%, ±3%). Sequential bins can have different nominal values, each separated by a percentage or a nominal value and asymmetrical limits. Binning parameters are also easily sorted to non-volatile RAM for quick setup in production environments.

The SR715/SR720 makes it simple to compensate for lead impedance and stray fixture and cable capacitance. The null calibration procedure, which takes just over a minute to perform, automatically corrects both open and short circuit parameters at all frequencies and all ranges. Null calibration should be performed after the fixture configuration has been changed, e.g. when the tweezers are added or removed. However, since the null calibration data is stored with instrument settings, it's easy to store calibrations for a number of different fixture configurations and quickly recall them later.

Rear Panel
Two rear panel input connections are provided for the external bias voltage. The bias supply should be floating and well filtered. The applied voltage must be 40 VDC or less, and current limited to 250 mA. This input is independently fused to protect the meter.

An optional handler interface provides control lines to a component handler for sorting. The interface has an input trigger line and output lines indicating bin-data available, busy and 10 separate bins. The connector is a male DB25, and uses open collector logic. A standard RS-232 interface allows complete control of all instrument functions by a remote computer. A GPIB interface is included with the handler option.

All non-ideal passive devices (resistors, inductors and capacitors) can be modeled as a real component (resistor) either in series or in parallel with a reactive component (capacitor or inductor). The impedance of these components change as a function of frequency. The series and parallel models are mathematically equivalent and can be transformed back and forth with the shown equations (see "Tech Note"). The SR715/720 can switch between either parallel or series equivalent circuits.

Usually one model is a better representation of the device under operating conditions. The most accurate model depends on the device and the operating frequency. Certain devices are tested under conditions defined by the manufacturer or industry standard. For example, electrolytic capacitors are often measured in series at 120 Hz in the C+R mode, so the ESR (equivalent series resistance) can be measured. The equivalent series resistance in capacitors includes things like dielectric absorption in addition to the ohmic losses due to leads. It is often listed on data sheets for electrolytic capacitors used in switching power supplies. At high frequencies, the ESR is the limiting factor in the performance of the capacitor.

The quality factor, Q, is the ratio of the imaginary impedance to the real impedance. For inductors, a high Q indicates a more reactively pure component. A low Q indicates a substantial series resistor. Q varies with frequency. With resistors, often all that is stated is that the resistor has low inductance.

The dissipation factor, D, is equal to 1/Q and is the ratio of the real impedance to the imaginary impedance. A low D indicates a nearly pure capacitor. D is commonly used when describing capacitors of all types.

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