Operation
The operation for measuring photodiode current is as follows:
1. Disengage both the
Bias
and
Amps/Watt
Engage
push buttons.
2. Select the range that includes the highest expected current to be measured. If this is unknown,
select the least sensitive range.
3. Before connecting the photodiode, adjust the
Offset Control
for a zero reading on the dis-
play.
4. Connect the photodiode to the instrument by means of the Input BNC connector.
5. Illuminate the photodiode with the light to be measured. The display will then indicate the mag-
nitude of the input current.
6. If a reading in units of Watts is desired, input the current responsivity of the detector by
depressing the
A/W Set
push button and adjusting the SET control knob until the desired value
is displayed. Depressing the
A/W Set
button will divide all subsequent readings by the
responsivity value and the units LEDs will switch to the appropriate value of Watts.
7. If reverse bias is desired, depress the
Bias Set
button. The bias voltage will then be dis-
played. Adjust the
Rotary Set Control
for the desired magnitude and polarity. Depressing the
Bias Engage
button will then apply this voltage in series with the photodiode.
NOTE: it is not
advisable to forward bias most photodiodes. Make sure that the bias is of the proper
polarity such that the detector is reverse biased.
8. If the display is blanked, the unit is indicating an over-range condition. Change the range to
progressively less sensitive ranges until the display indicates an on-scale reading.
9. If the
BAT LO
annunciator is activated on the LCD display, the batteries require charging. This
may be accomplished by plugging in the wall-mount power supply provided with the unit. The
instrument may be operated while the batteries are charging. Recharging requires about 14 hours
from a fully discharged condition. The microproccessor will automatically shuthe unit down if the
batteries are too low to be used.
10. If it is necessary to measure a small signal in the presence of ambient light, the
OFFSET
Control
may be used to null the background light to zero with the signal of interest turned off.
This subtracts the background illumination from the signal of interest. Note that detector noise
will increase with a large background signal.
11. High detector capacitance and/or cable capacitance will add add to the noise level.
-5-
Содержание PDA-750
Страница 6: ...4 PDA 750 Front Panel Controls...
