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Measuring fluctuating signals with the PSM2200 & PSM2201

The PSM range are real-time analysis instruments that simultaneously acquire and process data, once the input conditions are valid. The default set up conditions for each instrument are most suitable for measuring steady state, or slowly fluctuating signals – for rapidly fluctuating signals there are three areas where the response of the instrument can be improved using the menus or the communication commands:

1. Input ranging
2. Filtering
3. Frequency determination

1. Input ranging

All PSM units have input ranges spaced by a factor of about 3 (10mV, 30mV, 100mV etc.). If the input overdrives the selected input range then the measurement cannot be valid. The default ranging mode is full autoranging so the instrument will always find an appropriate range but measurements cannot be made during the autoranging process and data will be missed. To prevent this, the range can be fixed manually to the highest range that would be needed, either from knowledge of the maximum input signal, or by setting the ranging mode to autorange upwards only and running for a time to allow the highest range to be selected.

FunctionUsing menusUsing communications
To select the lowest range Press CH1 or CH2
Press DOWN to highlight
“minimum range” option
Press RIGHT or LEFT to select
Press HOME twice to exit
RANGE,channel,ranging,range
eg.
RANGE,CH1,MANUAL,10V
RANGE,CH2,UPONLY,100MV
To select the ranging mode Press CH1 or CH2
Press DOWN to highlight
“autoranging” option
Press RIGHT or LEFT to select
Press HOME twice to exit
RANGE,channel,ranging,range
eg.
RANGE,CH1,MANUAL,10V
RANGE,CH2,UPONLY,100MV
To quickly lock or unlock the
range
Press CH1 or CH2
Press STEP to toggle between:
manual, present range
full autorange, 10mV
Press HOME twice to exit
To reset the range when using
“autorange up” only
Press HOME*TRG

2. Filtering

The measurements from the PSM2200/1 are filtered equivalent to a first order low pass filter, nominally 1.5s at default settings (normal filter). The filter can be disabled, or it’s time constant can be increased (slow filter). To speed up the response of the instruments to step changes, the filter has an auto reset function that flushes the filter in the event of fluctuating results. If the input is noisy or rapidly fluctuating this may result in the filtering being reset for every result, so the filtering is ineffective. To disable this auto reset function, the filter can be set to “fixed time” so that every result is passed through the filter.

FunctionUsing menus Using communications
To select the filter type Press SETUP
Press NEXT until the menu
“ACQUISITION CONTROL” is
found.
Press DOWN to highlight “filter”
option
Press RIGHT or LEFT to select
Press HOME twice to exit
FILTER,type,dynamics
eg.
FILTER,NORMAL,FIXED
FILTER,SLOW,AUTO
To select the filter mode Press SETUP
Press NEXT until the menu
“ACQUISITION CONTROL” is
found.
Press DOWN to highlight “filter
dynamics” option
Press RIGHT or LEFT to select
Press HOME twice to exit
FILTER,type,dynamics
eg.
FILTER,NORMAL,FIXED
FILTER,SLOW,AUTO
To flush the filter when using
“fixed time” filtering
Press HOME*TRG

3. Frequency determination

In order to perform Fourier analysis (as used in Vector Voltmeter, LCR, gain/phase analyser, and other modes) the frequency needs to be accurately known. When using the instrument’s own generator, the frequency is known; when not using the instrument’s own generator (output turned off), the frequency is measured from the input signal on CH1. If the measured frequency varies then the instrument cannot make a measurement until it has determined a stable frequency. If using an external generator of known stable frequency, the PSM2200/1 can be forced to use the known frequency by enabling it’s generator at the same frequency (turn the output on but leave the output disconnected).

FunctionUsing menusUsing communications
To set a manual frequency Press OUT
Press DOWN to highlight
“frequency” option
Enter the known frequency and
press ENTER
Press DOWN to highlight
“output” option
Press RIGHT or LEFT to select
“on”
Press HOME twice to exit
FREQUE,frequency
OUTPUT,ON
eg.
FREQUE,2.4E3;OUTPUT,ON