Model 6517B Electrometer Reference Manual Section 3: Connections6517B-901-01 Rev. C / August 2015 3-7Low-noise input cablesTriaxial cables can generate enough triboelectric currents to corrupt the measurement. Thesecurrents are caused by friction between the center conductor and the inner shield when the cable isflexed or allowed to move around. The use of low-noise cables help minimize these triboelectriccurrents.The following low-noise cables are recommended for use with the Model 6517B: Model 237-ALG-2: This 2-meter low noise triaxial cable is terminated with a 3-slot male triaxialconnector on one end and three alligator clips on the other end. The alligator clip with the redboot is connected to the center conductor (input high). The black booted clip is connected to theinner shield (input low or guard). The green booted clip is connected to the outer shield (chassisground). Model 7078-TRX-3: This 3-foot low noise triaxial cable is terminated with a 3-slot male triaxialconnector at each end. Model 7078-TRX-10: This is the same as the Model 7078-TRX-3 except that it is 10 feet in length. Model 7078-TRX-20: This is the same as the Model 7078-TRX-3 except that it is 20 feet in length.When using cables, keep the following points in mind: For voltage measurements, the increased input capacitance caused by a long input cable cansignificantly slow down the reading response. To minimize this problem, always use the shortestpossible triaxial input cable and use guarding. For current and resistance measurements, the increased input capacitance caused by a longinput cable can result in noisy readings. To minimize this problem, always use the shortestpossible triaxial input cable and enable damping. Damping reduces the noise but it also slowsdown the response time of the measurement.Shielding and guardingThe following information covers the basics on using noise shields, guard shields, and safety shields.Noise shieldA noise shield is used to prevent unwanted signals from being induced on the electrometer input.Effective shielding encloses the circuit or device under test (DUT) and extends to the electrometerinput through a triaxial cable. The generic connection for the noise shield is shown in the figure below.Figure 18: Noise shield
