What'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.
Top
What
is the difference between ground and a groundable point?
The ESD Association standard
ESD S6.1-1999 defines ground as:
(1) A conducting connection, whether
intentional or accidential, between an electrical circuit
or equipment and the earth, or to some conducting body
that serves in place of earth.
(2) The position or portion of an electrical
circuit at zero potential with respect to the earth.
(3) A conducting body, such as the
earth or the hull of a steel ship used as a return path
for electric currents and as an arbitrary zero reference
point.
Example: Your third wire electrical
outlet
Groundable Point:
A designated connection location or assembly used on
an ESD protective material or device that is intended
to accommodate electrical connection from the device
to an appropriate ground.
Example: The snap on your worksurface
mat
Top
What is
the practical difference between measuring resistance
to ground and measuring inductance?
Inductance (L) is the current
(I) flow through a coil having of some number (N) turns
and the magnetic flux (ø) linked to the coil.
It is measured in Henry's (H) or mH, where
L= N(ø/I )
Resistance is the ratio of DC
voltage to Current passing between two electrodes, or
points, i.e., R = V/I.
In ESD control applications
we ask three questions (1) how much charge is generated?
(2) where does it go? - we want it to go to ground,
and (3) how quickly can it dissipate? Resistance to
ground is the opposition to current flow at a given
voltage. Thus, an accurate resistance (R) measurement
to ground (a) confirms a path to ground, and (b) depending
on the capacitance (C) of the discharging body, indicates
how quickly (t) a charge can dissipate to ground, i.e.,
t = RC, and 5t is the approximate total time in seconds
for dissipation.
Top
What
is the effect of humidity in ESD control circuit assembly
and test environments?
High relative humidity
(Rh) causes moisture to deposit and be absorbed by some
materials. It does not eliminate triboelectric charge
generation. Rather, it lubricates surfaces to reduce
charge generation to some degree, and helps render material
surfaces slightly more dissipative. The end result is
lower charge generation and a lower residual charge.
Unfortunately, Rh does not reduce charge sufficiently
on ordinary materials to protect many ESD sensitive
devices in critical assembly or laboratory areas. Never
design your ESD control based on available humidity.
Rather, design your ESD control
program assuming a low humidity (or no humidity) environment.
The if Rh is available, it helps make a good program
more effective. Like a special sauce heightens the flavor
of well-prepared dish.
Finally, relative humidity and
moisture will not eliminate charge. If it did, you would
never see lightening during a thunderstorm.
Top
My
PHT-770 Hygro-Thermometer jeeps displaying an "E2"
message. What does it mean?
An "E2" error
message represents a bad sensor. The message is displayed
continiously everytime the Hygro-Thermometer is turned
on.
Unfortunately, Prostat does
not repair or replace the sensor on the PHT-770. You
will need to replace it with our PHT-771 Digital Psychrometer.
To learn more about our PHT-771, click
here. If you wish to purchase one, please call our
sales department at +1 630-238-8883.
Top
What
does Constant Voltage mean for the PRS-801 and PRS-812?
Constant Voltage means
that the meter will put out the exact voltage is states,
regardless of the measurement. The advantage to this
is that a constant voltage meter is always recommended
in the test documents today. When something calls for
a specific voltage "while under load" this means the
meter MUST BE constant voltage.
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."
Top
|
| Training
