Filter
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5-11
Gain and Time Constant Menu
signal will obscure the signal at the reference and make detection difficult
if not impossible. See the SR850 Basics section for more information.
Man Reserve This key selects the Manual Reserve entry field for knob adjustment.
Keypad entry is not allowed for this parameter. This menu box is availa-
ble only if manual reserve is selected above. The reserve may be set
between the minimum and maximum values in 10 dB increments. The
min and max reserve limits change with sensitivity (see the table on the
previous page). If the sensitivity is changed, the manual reserve may
also be changed as described above.
Auto Reserve
Pressing [AUTO RESERVE] will change the reserve to manual and
adjust the dynamic reserve to the minimum reserve required. Auto
Reserve will not work if there are low frequency noise sources which
overload infrequently.
Time Constant This key selects the Time Constant as the active field. Use the knob to
adjust the time constant. Keypad entry is not allowed for this parameter.
The time constant may be set from 10 µs to 30 s (det. freq.>200 Hz) or
30 ks (det. freq. <200 Hz).
The maximum time constant is 30 s if the detection frequency is above
200 Hz and 30 ks if the frequency is below 200 Hz. The actual range
switches at 203.12 Hz when the frequency is increasing and at
199.21 Hz when the frequency is decreasing. The time constant may not
be adjusted beyond the maximum for the present detection frequency. If
the frequency is below 200 Hz and 100 s is the time constant and the fre-
quency increases above 200 Hz, the time constant WILL change to 30 s.
Decreasing the frequency back below 200 Hz will NOT change the time
constant back to 100 s.
The absolute minimum time constant is 10 µs. The actual minimum time
constant depends upon the filter slope and the DC gain in the low pass
filter (dynamic reserve plus expand). The minimum time constant is only
restricted if the dynamic reserve plus expand is high and the filter slope
is low - not a normal operating situation. The tables below list the mini-
mum time constants for the different filter slopes and gains.
6 dB/oct DC gain (dB) min time constant
<45 10 µs
<55 30 µs
<65 100 µs
<75 300 µs
<85 1 ms
<95 3 ms
<105 10 ms
<115 30 ms
<125 100 ms
<135 300 ms
<145 1 s
<155 3 s