SI-200 Differential Probe

DIFFERENTIAL PROBE SI-200
Calibration Procedure

This procedure is for use by qualified service personnel to adjust SI-200 properly. The equipments required are listed in Table 1

No.	Item	Minimum Requirements
1	Power Supply	6VDC/90mA or 9VDC/70mA mains adaptor or 4xAA cells or power lead.
2	DMM	DC Accuracy &lt 0.5%
3	Function Generator	Maximum Frequency >10MHz Sine-wave Distortion <1%
4	Oscilloscope	Bandwidth >= 20MHz Accuracy <= 2%

Table 1

This procedure is divided into following steps;
A. Prepare the probe for adjustment.
B. Adjust input bias voltage.
C. Adjust output offset voltage.
D. Adjust CMRR at 60Hz.
E. Adjust square-wave compensation for +input.
F. Adjust square-wave compensation for -input.
G. Adjust CMRR at 10MHz.

A. Prepare the probe for adjustment.

　A-1. Use a small flat screwdriver to peel the both panels off, referring to figure 1.

Fig. 1

　A-2. Loosen the four screws on the plastic cases.
　A-3. Remove the plastic cases. Figure 2 shows the location of adjustments on bottom side of the metal case.
　A-4. Connect the power source.
　A-5. Allow the probe and test equipments to warm up 20 minutes at an ambient temperature of 18 degree Celsius to 28 degree Celsius.
　A-6. In order to make following operation easier, use one plastic case to support the metal case and the input head.

Fig. 2

B. Adjust input bias voltage

　B-1. Connect the probe as shown in figure 3.
　B-2. The value of input bias voltage now is displayed on the digital multimeter.
　B-3. Adjust VR2 to make the input bias voltage as small as possible.
　B-4. The criterion is -2mV <= Vib <= +2mV.

Fig. 3

C. Adjust output offset voltage

　C-1. Connect the probe as shown in figure 4.
　C-2. Adjust VR3 for minimum output offset voltage.
　C-3. The criterion is -5mV <= Vout <= +5mV.

Fig. 4

D. Adjust CMRR at 60Hz

　D-1. Connect the probe as shown in figure 5.
　D-2. Set the output of the function generator to 20Vp-p 60Hz sine-wave, and set the input impedance of the oscilloscope to 50ohm. (Add a feedthrough 50ohm terminator to the input, if the oscilloscope doesn’t provide the 50ohm input impedance.)
　D-3. Adjust VR1 for minimum Vout displayed on the oscilloscope.
　D-4. The criterion is Vout <= 0.2mVp-p.

Fig. 5

E. Adjust square-wave compensation for +input.

　E-1. Connect the probe as shown in figure 6.
　E-2. Set the output of the function generator to 1.4Vp-p, 100KHz square-wave.
　E-3. Set the input impedance of the oscilloscope to 50ohm (Add a feedthrough 50ohm terminator to the input, if the oscilloscope doesn’t provide the 50ohm input impedance.)
　E-4. Adjust VC1 to make the front corner roll off or overshoot of the square-wave displayed on the oscilloscope less than 2.8mV.

Fig. 6

F. Adjust square-wave compensation for -input.

　 F-1. Connect the probe as shown in figure 7.
　F-2. Set the output of the function generator to 1.4Vp-p, 100KHz square-wave.
　F-3. Set the input impedance of the oscilloscope to 50ohm (Add a feedthrough 50ohm terminator to the input, if the oscilloscope doesn’t provide the 50ohm input impedance.)
　F-4. Adjust VC2 to make the front corner roll off or overshoot of the square-wave displayed on the oscilloscope less than 2.8mV.

Fig. 7

G. Adjust CMRR at 10MHz

　 G-1. Connect the probe as shown in figure 8.
　G-2. Set the output of the function generator to be 20Vp-p, 10MHz, sine-wave, and set the input impedance of the oscilloscope to be 50ohm (Add a feedthrough 50ohm terminator to the input , if the oscilloscope doesn’t provide the 50ohm input impedance.)
　G-3. Adjust VC1 slightly for minimum Vout displayed on the oscilloscope.
　G-4. The criterion is Vout <= 6mVp-p.

Fig. 8

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