Sutter Instrument BV-10, Operation Manual, Page: 22 / 38

BV-10 OPERATION MANUAL – REV. 3.00 (20180423)
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a 110-volt meter from a 220-volt source, you will need to supply a step down transformer.
Make sure that the connections are correct, particularly the ground, and that the
transformer can supply 0.1 amps at 110 volts. We cannot be responsible for incorrect use of
such devices by the user.
When choosing a location for your meter, you should consider that the meter's accuracy can
be affected by external noise sources. Large ungrounded conductive objects such as metal
bench tops or active noise sources such as motors or line cords may cause inaccurate
readings, particularly when measuring electrodes of high resistance. In addition, grounded
objects very close to the electrode may cause a decrease in reading for high resistance. Pay
particular attention to the method of mounting the electrode and the active lead. Use
materials with high electrical resistance, such as virgin Teflon, to avoid shunting the active
lead to ground.
3.2.1 Operation
There is no ON/OFF switch on the meter. This function is provided by the beveler unit when
the two are used together. In normal use, the meter can be left on during the course of a day's
work, but common sense dictates that the power should be disconnected when the unit is not
in use or will be unattended. For stand-alone operation you may wish to use a switched outlet
strip to provide an easy way to power-down the meter.
The meter should be left in the standby mode when not in use. This is particularly important
if the meter is to be shipped, since this helps protect the meter movement from mechanical
shocks. When you wish to make a reading, switch to the X5 range. If the reading is less than
100 Mohms, switch to the X0.1 range. This procedure will give the greatest resolution. When
you wish to disconnect the electrode, we recommend that the range select switch be returned
to the standby position.
3.2.2 Ohms Law – Theory of Operation
Ohm's law, V=IR, provides an obvious means for resistance measurement. If we force a
known current, I, through the unknown resistance, R, we can then measure the voltage drop,
V, across R and compute R as V/I. In practice, this is what the meter does. A controlled
current is forced through the electrode under test and the resulting voltage drop across the
electrode is measured. The current is in the form of a 12 Hz sine wave. This avoids the
problems caused by passing DC current without causing inaccuracy due to stray capacitance.
The peak amplitude of the current is 0.5 nA on the X5 range, 1 nA on the X1 range and 10
nA on the X0.1 range. Thus, the peak-to-peak voltage drop across a test electrode of 100
megohms on the X1 range would be 100 mV. For the other ranges, a full-scale reading will
also reflect a 100 mV peak-to-peak voltage across the test electrode. The meter provides
circuits to scale filter and average this voltage signal so that it produces a steady full-scale
deflection on the analog meter.
3.2.3 Accuracy
Each meter is calibrated for full-scale deflection at 500 megohms and 10 megohms using
precision resistors and should be /- 1%. Intermediate values are checked to assure
that the meter reads /- 1 minor division.
This level of absolute accuracy is more than enough for use in micropipette work since the
micropipette is far from being an ideal resistor that obeys Ohm's Law. In practice, the