The Fluke 341A and 343A differ only in the accuracy and resolution they provide. The 341 A offers 6-digit (10 pV) resolution with a basic accuracy of 50 ppm while the Model 343.4 is a 7-digit ( 1 uV resolution) instrument with a 20 ppm basic accuracy.
Cleanliness of the dc output is evident in the combined ripple and noise specifications of 50 pV rms from the 343A. Short term jitter and other random excursions are almost nonexistent (less than I ppm).
A simple amplifier/comparator circuit is utilized to establish a convenient variable current limiter. Any maximum current output from I to 30 mA may be set via a front panel control. In addition to providing for current protection of the load, a failsafe "crowbar" protects the series pass elements from damage should the total voltage across the elements exceed a safe level.