Specifications

Measurement Examples
18
1. Turn the SR400 off. Hold down the STOP (RESET) button while turning the SR400 on. Wait three seconds
and release the button.
2. Press the MODE key. Using the four arrow keys and the front panel knob, select the following parameters.
Unless otherwise indicated, leave all other settings at their default values:
T = TRIG TSET = 1E0
N PERIODS = 10 [AT 0]
AT N = STOP DWELL = 6E0 S
3. Press the A GATE key and select the following parameters:
A GATE = FIXED
A DELAY = 500 mS
A width = 500 mS
4. Press the LEVEL key and select the following parameters:
A DISC SLOPE = RISE
A DISC LVL = +150 mV
5. Using a function generator or a pulse generator, apply a 0.5 Hz, 5 V (TTL) signal to the TRIGGER INPUT
on the SR400.
6. Using a second signal source, apply a 10 kHz square wave (or pulse train) with an amplitude of
approximately 500 mV to the SIGNAL INPUT 1 on the SR400.
7. To view the COUNT PERIODS, press the MODE key and use the up/down arrow keys to display “N
PERIODS = 10 [at 0]”
Arm the counter by pressing the START button. (Alternatively, a TTL pulse applied to the START BNC on
the front panel will arm the counter.) Each measurement cycle should result in approximately 5,000 counts.
As an extension of the above example, the SR400 can be programmed to accumulate counts over numerous
gates. This is often done to improve the signal to noise ratio of low light level experiments. To accumulate
counts, set TSET (MODE menu) to the desired number of gates. For example, if you wish to accumulate over
five gates, set TSET – 5E0. In this case, six external triggers are required for each measurement cycle: five to
trigger the five gates and one to start the DWELL PERIOD. Any additional triggers received during the
DWELL PERIOD are ignored.