Modules - CAIRN RESEARCH - #19

_Package contents

The input amplifier can be configured to measure positive- or negative-going signals according to the setting of the jumper Jl. This jumper sets the polarity of the first amplification stage so that the output is always positive-going. The input impedance in either of these configurations is l MQ. Jl can also be used to select a virtual ground input stage configuration, in which the input stage acts as a current-to-voltage converter. This mode is intended for direct interfacing with a photomultiplier tube, and is the usual factory setting. The photomultiplier power supply should be negative with respect to ground, and the tube cathode connected to the negative supply. The tube anode is connected directly to the amplifier input on the front panel. In this mode the anode current is converted into a positive-going voltage in the input stage.

The gain of the input stage is set by J2, which is connected to the front panel H/L gain toggle on PMT amplifier version of the module. In either the positive or negative voltage mode configurations, the gain is either xl or xlO, and in virtual ground mode the gain is either O.lV or l.OV per microamp. This signal is coupled to the next stage via the front panel potentiometer, allowing the effective gain to be varied continuously down to zero from these limits. The amplifier stage following the potentiometer has a gain of xl, xlO or xlOO, according to the setting of J3. This gives a maximum overall voltage gain of xlOOO, or lOOv per microamp in virtual ground mode, which should be more than sufficient for all applications. The module is normally supplied with J2 and J3 both settoxlO.

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