497 AC Current Pre-amplifier
The 497, combining a six-decade trans-impedance amplifier and A to D convertor, has been developed to respond to two specific signal detection requirements, particularly pertinent in the testing of photovoltaic devices of various type.
In the DC mode it can be used as the main detection electronic, incorporating current amplifier and A to D convertor.
In the AC mode, it is used as a pre-amplifier for a lock-in amplifier 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 testing of PV devices.
Used in conjunction with the 496 lock-in amplifier, the 497 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, over which is passed the result from the A to D convertor.