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.
 

技术参数:
Signal Inputs
Bandwidth	DC to 300 MHz
Input impedance	50 Ω
Linear range	±300 mV (at input)
Input protection	±5 VDC, 50 V for 1 µs
Overload recovery	5 ns
Discriminators
Counters A, B, and T have independent discriminators when counting the signal inputs. All discriminator levels may be set to a fixed level or scanned.
Discriminator range	-300 mV to +300 mV
Discriminator slope	Rising or falling
Resolution	0.2 mV
Input offset voltage	<1 mV
Minimum pulse input	10 mV
Pulse-pair resolution	5 ns
DISC outputs	NIM levels into 50 Ω
Inhibit input	TTL high stops count
Trigger Input
Impedance	10 kΩ
Threshold	±2.000 VDC in 1 mV steps
Slope	Rising or falling
Protection	15 VDC, 100 V for 1 µs
Gate Generators
Both the A and B gates may be fixed in time or scanned. The gate outputs show the positions of the gates with respect to the discriminator outputs.
Insertion delay	25 ns
Maximum delay	999.2 ms
Minimum gate width	5 ns
Maximum gate width	999 ms or CW
Resolution	0.1 %, 1 ns minimum
Accuracy	2 ns + 1 %
Jitter	200 ps rms +100 ppm
Maximum trigger rate	1 MHz
GATE view output	NIM levels into 50 Ω
GATE view error	<2 ns
Scan and Dwell
The number of count periods or data points in a scan may be set from 1 to 2000. The duration of one count period is determined by the preset condition. The time between consecutive count periods is the dwell time and can be set from 2 ms to 60 s. The dwell output will be TTL high during the dwell time. This output can be used to trigger external devices. At the end of a scan (of 1 to 2000 count periods), counting may be programmed to stop or start the scan over again. The start key begins the first count period of the programmed scan. The stop key terminates the current count period and pauses the scan. If scanning, gates and disc levels are held at their current values. Pressing the stop key while in a paused condition will reset the scan, and all scanned parameters will return to their start values. Pressing the start key while paused resumes the scan by starting the next count period. The dwell time may also be set to external. In this mode, count periods begin with the start key or external start input (TTL rising edge). Count periods terminate with the preset condition, the stop key, or the external stop input (TTL rising edge). Pressing the stop key while not counting resets the scan. All count data is internally buffered for one scan. Data may be read over the computer interfaces during or after a scan.
Display Mode
Continuous	Displays current counter value
Hold	Displays final count value
D/A Output
The front-panel D/A output is proportional (linear or log) to A, B, A-B or A+B, and is updated at the end of each count period. There are two rear-panel D/A outputs: port 1 and port 2. These outputs may be set or scanned from the front panel or via the computer interface.
Full scale	±10 VDC
Resolution	12 bits (5 mV)
Current rating	10 mA
Output impedance	<1 Ω
Accuracy	0.1 % + 5 mV
General
Interfaces	GPIB and RS-232
Dimensions	16' × 3.5' ×13' (WHL)
Weight	10 lbs.
Power	35 W, 100/120/220/240 VAC, 50/60 Hz
Warranty	One year parts and labor on defects in materials and wor