Preamplifier vs. Pulser Input I'm using a Mesytec MPR-16-LOG preamplifier for some testing of gas ionization chamber. It has a 25 pin D connector input, in addition to an input labelled "Pulser In", that is a lemo connector input. I've never heard of a pulser input, what's it all about? 
http://www.mesytec.com/products/nuclear-physics/MPR-16-log.html 
 A: A pulser is a (usually off the shelf and sometimes battery driven) electronic debugging tool that emits a steady stream of pulses. 
The typical pulser emits one pulse per second in the logic format most often used with the physical layer cabling it couples to.
You use them for several purposes


*

*To check the functioning of lines and components of triggers and similar electronics. By observing the pulse before and after some portion of the trigger in an oscilloscope you can see if the edges are being degraded; if reflections are occurring in the part of the system you are testing; and measure that the timing delays actually occurring are those you allowed for in the trigger design.

*To select an unbiased sample of events. By triggering on the output of a pulser one gets a sample of the data coming into a detector that it not biased by decisions made in designing the usual trigger logic. This allows the measurement of efficiencies and tests to insure that important data is not being lost.

*As a means of measuring deadtime. The fraction of pulser pulses that actually generate a trigger is the livetime. If you need high precision, you generally use a separate scaler to count the pulses rather than counting on the pulser clock to be precise. (Hat tip: john in the comments.)

*As a means of evaluating and standardizing the gain in application such as multi-channel analyzers. (Hat tip: Jon Custer in the comments.)
In your case I imagine it is there so that you can measure the gain and the amplification delay.
