The April 1989 HP Journal is mostly dedicated to the 3458A and there's an article about the dual slope integrator starting on page 8. There's also a nice discussion about it in Art of Electronics 3rd Edition starting on page 918
HtH David -----Original Message----- From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of Attila Kinali Sent: 23 February 2018 15:51 To: Discussion of precise voltage measurement Subject: [volt-nuts] HP3458 ADC integrator Moin, I am trying to understand how the HP 3458 integrator of its dual-slope ADC works, as it's a bit more complicated than a simple, single opamp integrator. As you can see from the attached picture, it consists of 3 opamps (U1-U3) for the integrator itself, and another for the slope amplification (U4). Unfortunately, I do not get what U2 and U3 are doing, much less why they are needed. So I tried to simulate it in LTspice. But, the circuit oscillates. In both, the reset state (when the integration-C shorting switch is closed) and the integration state (though, less wildly so). I guess, this is because I replaced the LM6361 and AD848 by the LT1225 but do not understand why, or respectively, which of the differing parameters of the LT1225 causes this oscillations. Would someone be so kind and give me some hints? Thanks in advance Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
