SR510 Guide to Operation Front Panel

The front panel has been designed to be almost self-explanatory. The effect of each keypress is usually reflected in the change of a nearby LED indicator or by a change in the quantity shown on a digital display. This discussion explains each section of the front panel, proceeding left to right.

Signal Inputs

There are three input connectors located in the SIGNAL INPUT section of the front panel. The rocker switch located above the B input selects the input mode, either single-ended, A, differential, A-B, or current, I.

The A and B inputs are voltage inputs with 100 MΩ , 25 pF input impedance. Their connector shields are isolated from the chassis ground by 10Ω . These inputs are protected to 100V dc but the ac input should never exceed 10V peak. The maximum ac input before overload is 1V peak.

The I input is a current input with an input impedance of 1 KΩ to a virtual ground. The largest allowable dc current before overload is 1

∝A. No current larger than 10 mA should ever be

applied to this input. The conversion ratio is 106 V/A, thus, the full scale current sensitivities range from 100 fA to 500 nA with a max ac input before overload of 1 ∝ A peak. You should use short cables when using the current input.

Signal Filters

There are three user selectable signal filters available; a line frequency notch, a 2X line frequency notch, and an auto-tracking bandpass. Each of the filters has a pair of indicator LED's and a function key located in the SIGNAL FILTERS section of the front panel. Pressing a key will toggle the status of the appropriate filter. The status of each filter is displayed as IN, filter active, or OUT, filter inactive.

The notch filters have a Q of 10 and a depth of at least 50 dB. Thus, the line frequency notch is 6 Hz wide and the 2X line notch has a width of 12 Hz. Both of these filters can increase the dynamic reserve up to 50 dB at the notch frequencies. The achievable reserve is limited by the maximum

allowable signals at the inputs. The notch frequencies are set at the factory to either 50 Hz or 60 Hz. The user can adjust these frequencies. (See the Maintenance and Repair section for alignment details.) These filters precede the bandpass filter in the signal amplifier.

The bandpass filter has a Q of 5 and a 6 dB roll off in either direction. Thus, the pass band (between 70% pass points) is always equal to 1/5th of the center frequency. The center frequency is continually adjusted to be equal to the internal demodulator frequency. When the reference mode is f, the filter tracks the reference. When the mode is 2f, the filter frequency is twice the reference input frequency. The center frequency tracks as fast as the reference oscillator can slew and may be used during frequency scans. The bandpass filter adds up to 20 dB of dynamic reserve for noise signals outside the pass band, and increases the harmonic rejection by at least 13dB. (2nd harmonic attenuated by 13 dB, higher harmonics attenuated 6dB/octave more.) If not needed to improve the dynamic reserve or the harmonic rejection then the filter should be left OUT.

Sensitivity

The sensitivity is displayed as a value (1-500) and a scale (nV, ∝ V, mV). When using the current

input, which has a gain of 106 V/A, these scales read fA, pA, and nA. The two keys in the SENSITIVITY section move the sensitivity up and down. If either key is held down, the sensitivity will continue to change in the desired direction four times a second.

The full scale sensitivity can range from 100 nV to 500 mV. The sensitivity indication is not changed by the EXPAND function. The EXPAND function increases the output sensitivity (Volts out /volts in) as well as the resolution of the digital output display.

Not all dynamic reserves are available at all sensitivities. If the sensitivity is changed to a setting for which the dynamic reserve is not allowed, the dynamic reserve will change to the next setting which is allowed. Sensitivity takes precedence over the dynamic reserve. The sensitivity range of each dynamic reserve is shown below.

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