DIFFERENTIAL PROBE SI-51
Calibration Procedure
This procedure is for use by qualified service personnel to adjust SI-51 properly. The equipments required are listed in Table 1.

No Item Minimum Requirements
1 Power Supply 6VDC/90mA or 9VDC/330mA mains adaptor or 4xAA cells or power lead
2 DMM DC Accuracy < 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 1MHz.
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 topside and 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 VRA to make the input bias voltage as small as possible.
     B-4. The criterion is -3mV <= Vib <= +3mV.
 

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

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 620Vp-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 doesnˇ¦t provide the 50ohm input impedance.) 
      D-3. Adjust VR1 for minimum Vout displayed on the oscilloscope.
      D-4. The criterion is Vout <= 0.6mVp-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 40Vp-p, 1KHz square-wave.
      E-3. Set the input impedance of the oscilloscope to 50ohm (Add a feedthrough 50ohm terminator to the input, if the oscilloscope doesnˇ¦t provide the 50ohm input impedance.)
      E-4. Adjust VCA to make the front corner roll off or overshoot of the square-wave displayed on the oscilloscope less than 4mV    
 

Fig. 6
F.  Adjust square-wave compensation for -input.
      F-1. Connect the probe as shown in figure 7.. Referring to Fig. 7.
      F-2. Set the output of the function generator to 40Vp-p, 1KHz 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 VCB to make the front corner roll off or overshoot of the square-wave displayed on the oscilloscope less than 4mV.
 

Fig. 7
G. Adjust CMRR at 1MHz
      G-1. Connect the probe as shown in figure 8.
      G-2. Set the output of the function generator to be 20Vp-p, 1MHz, sine-wave, and set the input impedance of the oscilloscope to be 50ohm (Add a feedthrough 50ohm terminator to the input , if the oscilloscope doesnˇ¦t provide the 50ohm input impedance.)
      G-3. Adjust VC1 slightly for minimum Vout displayed on the oscilloscope
      G-4. The criterion is Vout <= 0.7mVp-p.
 

Fig. 8

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