Stanford SR570 Current Preamplifier
Low-noise current preamplifier (Distributed only in Germany.)
Filters
The SR570 contains two first-order RC filters whose cutoff frequency and type can be configured from the front panel. Together, the filters can be configured as a 6 or 12 dB/oct rolloff low-pass or high-pass filter, or as a 6 dB/oct rolloff band-pass filter. Cutoff frequencies are adjustable from 0.03 Hz to 1 MHz in a 1-3-10 sequence. A filter reset button is included to shorten the overload recovery time of the instrument when long filter time constants are used.
Input Offset and DC Bias
An input offset-current adjustment is provided to suppress any undesired DC background currents. Offset currents can be specified from ±1 pA to ±1 mA in roughly 0.1 % increments. The SR570 also has an adjustable input DC bias voltage (±5 V) that allows you to directly sink current into a virtual null (analog ground) or a selected DC bias.
Toggle and Blanking
Two rear-panel, opto-isolated TTL inputs provide additional control of the SR570. A blanking input lets you quickly turn off/on the instrument’s gain which is useful in preventing front-end overloading. A toggle input inverts the sign of the gain in response to a TTL signal allowing you to perform synchronous detection with a chopped signal.
Battery Operation
Three rechargeable lead-acid batteries provide up to 15 hours of battery-powered operation. An internal battery charger automatically charges the batteries when the unit is connected to the line. The charger senses the battery state and adjusts the charging rate accordingly. Two rear-panel LEDs indicate the charge state of the batteries. When the batteries become discharged they are automatically disconnected from the amplifier circuit to avoid battery damage.
No Digital Noise
The microprocessor that runs the SR570 is "asleep" except during the brief interval it takes to change the instrument’s setup. This ensures that no digital noise will contaminate low-level analog signals.
RS-232 Interface
The RS-232 interface allows listen-only communication with the SR570 at 9600 baud. All functions of the instrument (except power on) can be set via the RS-232 interface. The RS-232 interface electronics are opto-isolated from the amplifier circuitry to provide maximum noise immunity.
