Keithley 2563 Noise in Low Curr free download

File name 2563 Noise in Low Curr.pdf

A G R E AT E R M E A S U R E O F C O N F I D E N C E Problem: Noise in Low Current Measurements Low current measurements (current <1nA) Potential Cause: Vibration C. A useful alternative to the series resis- often encounter noise. Here are a few likely Vibration can cause noise currents to flow tance is to put a forward-biased diode in causes of noise in low current measurements due to the triboelectric effect. series. The diode acts like a variable re- and how they can be avoided. sistance--low when the charging current Remedies is high and then increasing in value as the Potential Cause: A. Use low noise cables, which have graph- current decreases with time. Electrostatic Coupling ite lubrication on the shield braid, to cut This occurs when an electrically charged down the friction between insulators in object is brought near an uncharged object. the cable to reduce this effect. Potential Cause: B. Secure the cables to avoid any unneces- Offset Current Drift Remedies sary vibration. Offset currents can drift over a period of A. Shield the device/circuit--High imped- time, usually because of temperature chang- ance materials do not allow the charge Potential Cause: es in the device and the meter. to decay quickly. Shielding the device or Low Source Impedance circuit to be measured greatly reduces the Remedy electrostatic interference. Connect the Remedies Stabilize the temperature of the meter, shield to circuit low. A. When the impedance of the source is low the device, and the general environment of B. Movement--Avoid movement and vibra- a less sensitive measurement range can be the measurement. tion near the test area. used. C. Keep all charged objects (including peo- B. Adding some series resistance when meas- ple) and conductors away from sensitive uring current from a capacitive source re- areas of the test circuit. duces noise. Specificat