Scitec 420 - 8 Using the 420 as a Single Phase Instrument to Take Accurate Measurements

Boston Electronics Corporation, 91 Boylston Street, Brookline MA 02445
(800)347-5445 or (617)566-3821 * fax (617)731-0935 * boselec@boselec.com * www.boselec.com
Bartles Industrial Estate, North Street, Redruth, Cornwall TR15 1HR
Tel. (01209) 314608 E-mail: scitec@scitec.uk.com
Fax. (01209) 314609 Web: http://www.scitec.uk.com
8 USING THE 420 AS A SINGLE PHASE INSTRUMENT TO TAKE
ACCURATE MEASUREMENTS
This series of instructions uses the 420 as a single phase lock-in amplifier and just uses the X
channel.
This method uses the fact that when the instrument is correctly set up, adjusting the phase by
±90° will set the output to 0 and by adjust the phase by 180° will invert the output.
(1) Connect up the lock-in amplifier.
(2) Switch the offset control (6) to off.
(3) Switch the 1F/2F switch (11) to that required.
(4) Switch the input sensitivity (1) to 1V.
(5) Switch the time constant (3) to 100mS.
(6) Switch both phase controls (9)(10) to 0°.
(7) Switch the output select switch (7) to X.
(8) Increase the sensitivity control (1) until a signal is seen at the output (13).
(9) If the output becomes noisy, increase the time constant setting (3) until the noise is
removed.
(10) Adjust the phase control dials (9)(10) until a maximum output is seen.
(11) Subtract 90° from the phase shift by turning the coarse phase control (9) by one position
anticlockwise (or 3 positions clockwise to 90° if at 180°)
(12) Take a measurement of the output.
(13) Add 180° to the phase shift by turning the coarse phase control (9) by two positions.
(14) Take a measurement of the output.
(15) Use the fine phase control (10) to adjust the outputs so the signal levels seen in (12) and
(14) above are the same.
(16) Hopefully the signals seen in (12) and (14) above are both 0V. If this is not the case switch
on the offset control (6) and adjust the X offset control (4) until both signals are 0V. The
fine phase control dial (10) can be used to remove a positive voltage on one output and a
negative voltage from the other. The X offset control (4) can be used to remove either a
positive voltage or negative voltage on both outputs.