GENERAL The Keithley Model 150B Microvolt Ammeter is an extremely sensitive instrument which measures voltages from 0.3 microvolt to 1 volt and currents from 0.3 nanoampere to 1 mi 11iampere. It can be used as a voltmeter, null detector or an ammeter with either battery or line power operation. AS A MICROVOLTMETER. a. The Model 150B is ideal as a microvoltmeter for measuring semiconductor resistivity, thermopile and thermocouple potentials, Hall effect, contact resistances, biologically generated emf's, electrochemical potentials and strain guages emf's. b. The Model 150B has input noise less than 25 nanovolts peak-to-peak; high input resistance and low zero shift; excellent zero stability; very high 1ine-frequency rejection and common mode rejection; battery operation; zero suppression; special low-thermal input circuitry; two available outputs. c. With these features, the Model 150B permits excellent resolution; maintains measurement accuracy even from high resistance sources; is ideal for long-term measurements; detects dc signals in the presence of large ac voltages and is virtually insensitive to ac or dc voltages applied between circuit and chassis ground; disconnects from power lines for improved isolation; measures small changes in dc signals; reduces temperature and shielding problems; provides outputs where either filtering is needed or fast response or greater output power is needed. AS A NULL DETECTOR. a. As a null detector the Model 150B is excellent for use in ratio measurements and in potentiometer and bridge circuits. b. The Microvolt Ammeter's outstanding features as a null detector are: very good resolution; high line frequency and common mode rejection; isolation from chassis ground to input terminals; battery operation; high input resistance; floating capability; low zero shift; zero suppression. c. Because of these features the Model 150B has resolution comparable to the maximum usable resolution of most potentiometers and bridges; may be simply connected to the terminals of a null circuit; is very insensitive to common mode voltages developed in the null circuit; can be used in most potentiometer and bridge circuits without off-null loading; accurately detects a null regardless of the setting on most potentiometers and bridges; compensates for thermal emf's generated in the null circuit. AS AN AMMETER. a. The Model 150B has general use in research, design and production test facilities. It is useful for making low voltage drop, in-circuit measurements as well as measuring the output of radiation detectors, phototubes and other current generating transducers. b. The instrument has low voltage drop for measuring currents in very low-voltage circuits low zero drift for measuring long-term current; excellent floating capabilities for measuring ungrounded sources; and low input noise, giving excellent resolution.