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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.

SPECIFICATION
Inputs 2, remotely/manually selected
Gain ranges 103 - 108 V/A
Maximum input 10mA
Frequency response See table below
Input impedance Virtual ground
Gain accuracy +1%
Gain stability 200ppm/oC
Output stability 5ppm/oC to 500ppm/oC depending on sensitivity
Interface USB (via 417/417T mother unit)
ADC Resolution 4½ digit BCD (0 - 19999) i.e. 14 bit resolution
ADC Conversion 100ms
ADC Input range -0.2V to 9.8V
Linearity <0.025% departure from linearity from zero to full scale
V/A Bandwidth (-3Db)
103 >1MHz
104 1MHz
105 260kHz
106 30kHz
107 23kHz
108 4kHz