The SR400 Dual-Channel Gated Photon Counter offers a convenient, integrated approach to photon counting that avoids the complexity and expense of older counting systems. No longer is it necessary to mix and match amplifiers, discriminators, gate generators and counters. The SR400 combines all these modules into a single, integrated, microprocessor controlled instrument. Complex measurement tasks such as background subtraction, synchronous detection, source compensation and pile-up correction can all be performed easily with the SR400.

Counters

The SR400 has two independent channels that can count at rates up to 200 MHz. Different counting modes allow you to count for a fixed amount of time, until a certain number of counts have been received, or for a fixed number of triggers. Each counting channel has its own gate generator providing counting gates as short as 5 ns or as long as 1 s. The gates can be set in a fixed position relative to the trigger signal, or scanned to measure lifetimes or recover time-varying waveforms.

The actual inputs to the counters can be viewed as NIM level pulses from the discriminator outputs on the front panel. The discriminated pulses are negative going from 0 to -0.7 V. The DISC outputs are very useful when adjusting discriminator thresholds or gate timing.
SR400 Block Diagram

Signal Inputs and Discriminators

Both analog signal inputs (A and B) are internally terminated into 50 Ω. The inputs accept signals between ±300 mV and are protected to ±5 VDC. Each input is followed by a DC to 300 MHz amplifier, allowing detection of pulses as small as 10 mV. If additional sensitivity is required

Parameter Name	Parameter Value
Type	photon binary
Display	digital
Technology	electronic