AH 2700A
16Pages

AH 2700A 50Hz-20kHz Ultra-precision Capacitance Bridge World's Most Accurate 50Hz-20kHz Capacitance/Loss1 Bridge The AH 2700A offers unparalleled stability, resolution, linearity and accuracy in a multifrequency capacitance/loss1 bridge (whether manual or automatic). Its numerous state-of-the-art features make it an exceptionally user-friendly instrument. The precision of the AH 2700A is creating new applications in calibration, science, and production in a wide range of fields. • Selected Performance Specifications • Measures extremely low loss down to a dissipation factor of -8 -7 1.5x10 tan 5, a conductance of 3x10 nanosiemens or a resistance up to 1.7xl06 gigohms • As little as 0.4 second required for full precision measurements and as little as 30 ms required for repeated measurements on the same DUT • NIST traceable calibration • IEEE-488 GPIB and IEEE-1174 serial interfaces included; remote device can act as controller or logger • Automatic internal calibration LabView Driver Monitoring of calibration due date and temperature status • Deviation Mode with Fast Analog Output has a frequency response of 4.2kHz at 3 dB down Continuous Frequency (Option C) is now available Synchronous Rejection (Patent No. 6,987,391) eliminates virtually all power line related interference working in conjunction with conventional commutation (test signal reversal) Negative capacitance and loss ranges measure negative values to allow for unusual DUT’s or three terminal networks Three terminal BNC connections minimize connector costs and number of cables Programmability can eliminate need for external controller Large, variable-brightness displays have 8 digits for capacitance and loss and 5 digits for frequency Zero mode compensates for test fixture capacitance and loss External DC bias may be applied up to ±100 volts • External trigger capability Self-test diagnostics on power-up and by command • Autoranging Three year warranty The term "loss" is used to refer to the component of the impedance which is 90° out of phase with respect to the capacitive component. The AH 2700A can report loss in units of conductance, dissipation factor, series or parallel resistance, or loss

BASIC DESIGN The AH2700A measures capacitance and loss in medium- and high-impedance ranges, and thus allows using three-terminal rather than five-terminal connections to the DUT (Device Under Test). Its unmatched precision is the result of a uniquely designed ratio transformer which is the culmination of over 40 years of bridge design and manufacture. Equally important is the unique temperature-controlled, fused-silica capacitance standard which allows extremely high measurement stability and immunity to mechanical shock. These elements combine to form a true bridge operating at 50 Hz - 20...

Measurement Errors Measurement troubles are easily pinpointed by one of over a dozen English language error messages (or, optionally, error codes). Additionally, many other command and status messages are reported. Calibration A unique calibration technique allows internal precision components to be compared against internal temperature-controlled standards with the appropriate corrections being made by a microprocessor. The AH2700A also provides for calibration against external standards. To prevent unauthorized calibrations, a passcode (which only the manager of the instrument can change)...

The reaction of many technical persons upon first learning of the AH2700A is: "That's a very impressive instrument, but we don't see a need for such precision in our work. Furthermore, such measurements must be more difficult to make." Until the introduction of the original AH2500A, this attitude toward high precision capacitance measurements was justified. Previously, the only commercially available instruments were manually operated, required a skilled operator to spend several minutes balancing the bridge, were prone to reliability problems due to the large number of open switching...

The specifications are grouped according to whether the DUT is modeled as a resistor in parallel with a capacitor or in series with it. is the value of the measured (parallel) capacitance in picofarads (pF= 10-12 F). Also used are attofar-ads (aF = 10-6pF) and femtofarads (fF = 10-3pF). is the value of the measured loss expressed as a conductance in nanosiemens (nS = 10-9 S). is the value of the measured loss expressed as a dissipation factor (tan 8). D has no units. is the value of the measured loss expressed as a parallel resistance in gigohms (GQ = 109Q). is the value of the measured...

Figure 2. The values of Cs and Rs are measurable in the six shaded regions. In five of these regions, one or both of the measured values are too large to report on the AH2700A’s display. In three of these five regions, one or both values are also too large to send to any remote devices. The table below shows what can be reported in each region. A "Display" entry means that the result can be shown on the instrument’s display. A "Remotes" entry means that the result can be reported to an IEEE-1174 or IEEE-488 device. Cs Display & Remotes Display & Remotes Display & Remotes Remotes only...

Table 1. Capacitance and conductance ranges for the preferred limiting voltages with f a 1 kHz. For f < 1 kHz, multiply Limit by f in kHz. At and Ac are used by the specification equations. Limit Capacitance range Resolution in absolute units:* Parallel: where nc = 1.4t-1/2 and nv = 0.0l(1+0.1/f)(RS+l0)l/2(1+D2)l/2t '1/2. Ac is found in Table 1. The series resistance Rs needed for nv may be calculated using Rs= Dxl06/(mC(l+D2)). ♦Resolution is the smallest repeatable difference in readings that is guaranteed to be measurable at every capacitance or loss value. Useful resolution is typically...

Non-linearity is the deviation from a best fit straight line through a plot of the measured quantity versus the actual quantity. The test signal voltage is assumed to be constant. Accuracy in ppm following calibration: Parallel: ⎧ ⎧ 1.5 f2 1700 1 1 1 -C: ± ⎨ 1 8 + -- + f + ------- 4 + -- + 200D + -------- 1 + ----------------------- + A T f + -- + ⎨ 3 ×10–6 f ⎩2 The length of the cables connecting the 2700A to the DUT has a negligible effect on the accuracy for small capacitances. This assumes that the coaxial shield on these cables has 100% coverage. If uncorrected by the CABLE command,...