BNC 6040 - Manual (Page 57)

57
MAINTENANCE AND CALIBRATION
Rep Rate Check
Remove any plug-in module. Connect the TRIG OUT to channel B of the Time Interval Counter (TIC).
Select the Internal Trigger parameter with the {TRIG} key. Set the rep rate for
5.000 MHz. Now set the rep rate for 4.999 MHz and check that the frequency is between 4.9990 and
4.9992 MHz.
External Trigger Circuit
The external trigger circuit requires calibration of the DAC (Z4) and its associated amplifier
(Z7).
Refer to Schematic 6040-32. The first step measures the attenuation factor (approximately x 2) of the
trigger input termination network R78. 79. 80 and 81. Apply approximately 1.9 V dc to the TRIG IN
connector and record both this voltage (Vin) and the voltage at Z13-3 (Vs). Calculate Vin/2Vs = A.
Record A (typically 0.97-1.03). Disconnect the dc voltage from the instrument.
The next step calibrates the DAC including the actual value of A. With the front panel pushbuttons, set
the external trigger level to +2.5 V. Calculate 1.35 x A - B and record (typically B = 1.35 V). With R4, set
the voltage at Z7-7 to equal B. Change the display to -2.5 V and with R7 set Z7-7 to B. This completes
the calibration of the external trigger circuit.
Pulse Out Amplifier
As the performance of this unit is in part dependent on the correct adjustment of the PULSE OUT
amplifier this should be performed next, as follows.
Set the 6040 to generate pulses at approximately 1 MHz in the Single Pulse setting. Set the Width to
100 ns. Connect a 50-ohm cable between TRIG OUT and the scope EXT TRIG input and also from
PULSE OUT to the scope vertical input. Check to be sure that the 50-ohm input impedance (not 1 Meg)
is used.
1. Set R17 and R23 at midrange.
2. Observe PULSE OUT and set R17 for minimal ringing and edge distortions.
3. Set R23 for an amplitude of 5 V ±0.2 V.
Delay Oscillator
Connect the TIC (HP 5370) as follows: Start input to TRIG OUT and Stop input to PULSE OUT (both
inputs terminated in 50 ohms and both slopes to +). Set the TIC for "TIM" and 100 samples and adjust
the trigger levels for best triggering (set attenuator to XI for Start and XI0 for Stop). Set the 6040, using
the front panel controls, for internal trigger rate of 90 Hz, a delay of zero and a width of 30 ns. Press the
Set Reference button of the TIC. Reset the delay to 10 ms and adjust RIO for 10 ms.