QWhat's the difference
between a constant voltage meter and a non-constant
voltage meter?
Constant voltage instruments
are engineered to apply a specific voltage and hold it
within a defined tolerance during a measurement, regardless
of the resistance being measured.
Benefits
of constant voltage measurements are greater accuracy
and reproducibility, consequently laboratory instruments
are typically constant voltage types. Prostat's PRS-801 and PRS-812 resistance instruments provide constant
voltage measurements of 10 volts and 100 volts ±
< 5 millivolts.
A non-constant voltage meter
is an instrument that varies test voltage based on the
resistance of the load under test. Meaning that if the
resistance of the material being tested is low, the
test voltage of a typical open circuit instrument will
automatically decrease.
For example, when measuring
resistance of 109 or greater, a typical instrument
may provide a test voltage of 100 Volts. However, the
same instrument when measuring 107 ohms,
may provide 65 Volts or less; and when measuring in
the mid 105 range, the instrument may supply
less than 20 Volts.
For performance specifications
refer to the PRS-801 or PRS-812 data sheets.
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QWhat does Constant
Voltage mean for the PRS-801 and PRS-812
Constant Voltage means
that the instrument will supply test voltage under load. The advantage to this
is that a constant voltage meter is most accurate and repeatable and is recommended
in standards documents.
ANSI/ESD S7.1-2005 - Floor
Materials, Characterization of Materials
Page 2
Section 5.0 EQUIPMENT AND MATERIALS
5.1.1.1.1
"Use of Laboratory Evaluation Meters: The meter(s)
shall have an output voltage, while
under load, of
10 volts (+/- 5%) for measurements less than 1.0x106 ohms, and 100 volts (+/- 5%) for measurements of
1.0x106 ohms and above..."
In Addition
Page 3
Section 6.1 LABORATORY EVALUATIONS
"For all laboratory evaluation the meter specified
in 5.1.1.1.1 shall be used..."
Page 4
Section 6.2
...in case of dispute or disagreement the meter described
in section 5.1.1.1.1 (Laboratory Evaluation Meter) shall
be used."
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QWhat is the
current that the PRS-801 and PRS-812 inject onto the "material-under-test"?
The PRS-801 and PRS-812 measure current then calculate resistance based on test voltage. i.e., ohms
law: Test Voltage/Current = Resistance. Current flow during the measurement
is a function of the material under test's resistance.
The
PRS-801 and PRS-812 are not "open circuit" meters, they are precision constant
voltage, similar to laboratory level instruments.
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