Keithley 610B Instruction Manual page 14

OPERATION
8fom.s 610~) 610~~ ELECTROMETERS
Connect the unknown source to the INPUT Receptacle and unlock the ZERO CHECK
Button.
Set the METER Switch to + or -, as necessary. Increase the sensitivity
with the Multiplier Switch,
Recheck the zero setting after increasing the sen-
sitivity.
c. Low Impedance Measurements.
To decrease the input resistance from 1014 ohms,
set the Range Switch to one of the AMPERES ranges.
The input resistance is now
the reciprocal of the current range. For instance,
to obtain an input resistance
of
107 ohms - which is normal for conventional VTVMs - set the Range Switch
to the 10-7 AMPERES range.
Set the full-scale voltage range with the Multiplier
Switch.
Operating procedures are the same as subparagraph b above.
d. To measure sources more than 100 volts, use the Model 6102A 1O:l Divider
Probe or the 6103A 1OOO:l Divider Probe. The Model 6102A extends ths Model
610B's range to 1000 volts;
1010 ohms.
overall accuracy is *3% and input resistance is
The Model 6103A extends the Model 610B's range to 30 kilovolts;
overall accuracy is C5% and inputresistanceis 1012 ohms.
Follow the same
operating procedures with the dividers as in subparagraph b.
The full-scale
voltage range is the divider ratio times the Wltiplier Switch setting.
Accuracy decreases 0.5% when the center zero scales are used
because the scale span is shorter.
2-6.
Currant Mearuremantr.
a.
The Model 610B can measure currents three ways.
1. In the normal method - used on any range
-. the current is determined
by measuring the voltage drop across a resistor shunting the amplifier input.
This method is useful when lower noise is more important than faster response
speeds or if some damping is needed.
2.
In the fast method - for use only below the lO-5 ampere range -
the shunt resistor is between the amplifier output and input in the feedback
loop. This circuit largely neutralizes
the effect of input capacity and
greatly increases the response speed. Also, the input voltage drop is reduced
to a maximum of one millivolt on any range.
3. For galvanometric current measurements,
the Model 610B acts as a null
indicator between a very accurate current source and the unknown current source.
b.
Rise time varies primarily with the currant range, theinput capacity
and the method used. On most ranges, the rise time is less than one second with
50 picofarads across the input.
Even with much larger shunt capacities, the
negative feedback maintains a short rise time. Given a choice, it is better to
place the Electrometer near to the current source than to the data reading in-
strument. Transmitting the fnput signal through long coaxial cables greatly de-
creases the response speed and increases noise due to the cable capacitance.
c. Normal Method (0.3 to LO-l4 ampere ranges).
1. Follow the instructions of paragraph 2-4. Set the controls as follows:
10
1064R