Signal Input - Stanford Research Systems SR865A Operation Manual

Signal Input

Input [Select]
The Input [Select] key selects between the voltage and current preamps.
The voltage inputs (A and B) have a 10 MΩ, 25 pF input impedance. Their connector
shields are isolated from the chassis by either 10 Ω (Ground) or 10 kΩ (Float). Do not
apply more than 10 V to either input. The shields should never exceed 1 V.
The current input uses the I connector. The input burden resistance is 100 Ω (1 µA range)
or 1 kΩ (10 nA range) to a virtual ground. The largest allowable current before overload
is around 3 µA (1 µA range) or 30 nA (10 nA range). No current larger than 10 mA
should ever be applied to this input.
Voltage [A−B]
The voltage input can be either a single-ended (A) or differential (A−B) voltage. The
shields of A and B are connected and grounded by either 10 Ω (Ground) or 10 kΩ (Float).
Voltage [Couple]
This key selects the voltage input coupling. The signal input can be either ac or dc
coupled. The ac coupling option uses a high pass filter to pass signals above 160 mHz
and attenuate signals at lower frequencies. ac coupling should be used at frequencies
above 160 mHz whenever possible. At lower frequencies, dc coupling is required. ac
Operation
SR865A DSP Lock-in Amplifier
65