Philips PM6302 Instruction Manual page 12

12
2.2.3.1. Searching the correct measuring range in case of unknown capacitance value
— Depress push-button "SEARCH"
— Switeh over the measuring ranges
— The correct measuring range is found when the indicator points to the "Ww7"-field
— Pointer deflection too small — select a lower measuring range
-~ Pointer deflection too large —> select a higher measuring range.
2.2.3.2. Measuring the capacitance and the loss factor D in case of a known measuring range
— With the vernier adjust the pointer deflection to a minimum.
— With potentiometer "Q/D" adjust the loss factor D so that a better minimum is obtained
- Repeat this two adjustments alternately for the lowest minimum
— If no clear minimum can be reached, depress push-button "D"" (D < 1.4; measuring frequency 100 Hz) and
repeat the procedure above.
— Multiply the scale reading by the value selected with the range selector to obtain the exact capacitance value.
— To obtain the loss factor D = tag 6 read the value adjusted with potentiometer "Q/D" and multiply it by
0.01 or 0.1 depending on the position of push-button "D"
— When measuring smailer capacitances sudstract the initia! capacitance of this instrument from the measured
value. The initial capacitance can be measured, when no sample is connected to sockets ''1-E"'.
Note: {f, when measuring smaller capacitances, no correct minimum can be adjusted, eventually screen the
sample for external mains stray fields.
2.2.3.3, Measuring capacitances with formation voliage A
In order to form electrolytic capacitors and in case of capacitance measurements with d.c. bias voltage for the
sample, a mains-independent battery can be connected to sockets DC-BIAS" at the rear. The short-circuit
plug must then be removed.
Pay attention for the polarity of the sample: +°° —> "1"; ""—"" —> "E""
The a.c, internal resistance of the battery must be low; i.e. under certain circumstances a capacitor Cp must be
connected in parallel with the battery; the value of Cy should be higher than or equal to the sample capacitance;
but it must be at least 100 j4F (see Fig. 5).
In order to protect the measuring bridge, the d.c. current from the battery must be limited by a resistor Rv.
The resistance must be at least 50 Q per volt of the supplied d.c. voltage (see Fig. 5),
For measuring the capacitance and the loss factor of the sample see 2.2.3.1, and 2.2.3.2.
2.2.3.4, Measuring junction capacitances
In order to measure the junction capacitance of a varicap, proceed as follows:
— Supply an adjustable d.c. voltage from a mains-independent galvanic battery and connect an external a.c.
voltage source to the bridge supply conform to figure 6.
— Connect the sample with the cathode to terminal | and the anode to terminal E.
By stepwise changing the d.c. voltage and measuring the capacitance of the varicap in accordance with
2.2.3.1, and 2.2.3,2., the characteristic of the semple can be determined.
Note: The voltage of the external bridge supply should not be higher than 1 V, in order to avoid faulty
measurement by overloading the sample.
2.2.4, Measuring inductances
— Depress push-button "L"
— Connect the sample to sockets "$-E"
2.2.4.1, Searching the correct measuring range in case of unknown inductance value
— Depress push-button "SEARCH"
— Switch over the measuring ranges
— The correct measuring range is found when the indicator points to the "WA "field.
— Pointer deflection too small —— select a lower measuring range
— Pointer deflection too large ——> select 2 higher measuring range
~ For inductances with smalier Q (< 1) the searching procedure can indicate a range which is one decade too
low.