477 AC Current Pre-amplifier
The 477 is used as a pre-amplifier for a lock-in amplifier in AC systems employing current source detectors such as photomultipliers and photodiodes which, at low frequencies, give their best performance when connected to a virtual ground.
The virtual earth inputs (two) of the amplifier ensure that the detector is kept in short circuit condition, whereby no voltage is generated across the detector as a result of the photocurrent it produces. This short circuit operation enhances the linearity of detectors, reduces the effect of cable capacitance and is often a necessary condition in the determination of detector responsivity.
Used in conjunction with the 496 lock-in amplifier, the 477 allows the user to select a combination of current and voltage gain which optimises the trade-off of noise performance versus DC current sinking.
Gain range and input in use may be selected via the USB interface.
The 477 is a single-width module, housed within the 417/417T base unit.
- Virtual ground input
- 2 inputs with programmable selection
- 6 programmable transimpedance ranges
- USB interface (via 417/417T base unit)
- Overload indication given over bus