Digital Micron Gauges; Inaccurate Readings; Erratic Readings - JB INDUSTRIES ELIMINATOR DV-3E Manual De Instrucciones

Charging lines have been used for many years for the vacuum end of air
conditioning and refrigeration servicing Charging line use stretches back as far as
when inches of Mercury (inHg) was the way measuring of a vacuum on a system
was taught A charging line hose can be vacuumed to 50 microns if it is clean New
environmental hoses, fresh off of the shelf, will only reach about 300 microns until
they are cleaned out with alcohol and vacuumed out for a while Why is this? First,
the charging lines are mostly gaskets made for positive pressure Second, they are
permeated See page 7 for how permeation occurs
The only vacuum tight hose is a flexible metal hose Third, the compound of
the hose inside will out-gas when under a vacuum until it is cleaned out, as
discussed earlier
If you are used to using a compound gauge when testing for a leak or holding
a vacuum, using a digital gauge will be a little tricky the first time you use it JB
digital vacuum gauges will display microns jumping up and down in measure
You might think that the gauge is erratic or that there is a leak in the system The
reason for the changing microns is due to a whole other area of understanding the
environment inside a system being vacuumed We will discuss this event in the
next section on Digital Micron Gauges
To help show the difference of a digital and analog displays in microns, and a
compound gauge display in inches of mercury (inHg) as it relates to their displays
of vacuum, we need to hook them up Take a compound gauge and a digital micron
gauge, and an empty refrigerant tank This hook-up is illustrated on the next page
(Figure16) This allows you to demonstrate the four components in holding a
vacuum: the connections, the volume, the depth of vacuum, and the length of time
that volume is in deep vacuum
Link both gauges together by solid brass adapters and o-ring couplers and couple
to the tank The tank is connected by an o-ring coupler to one of the intake ports
of the pump by way of braided metal hose with o-ring connections Then, with
the isolation valve in the open position, we can begin to vacuum this hook-up
and watch the readings on the various gauges move into deep vacuum Within
seconds, the compound gauge' s needle should be nearing 27-29" while the digital
and analog gauge readings are still heading into deeper microns
After the digital gauge reaches 500-600 microns, close the isolation valve You will
see the digital reading start a pretty rapid rise in micron readings Notice that the
compound gauge' s needle has not moved
NOTE: If the compound gauge' s needle does move toward zero on the scale, you
have an air leak in your connections Open the isolation valve again and this time
let the hook-up vacuum for 5 minutes Then close the isolation valve again and
watch Open the isolation valve for about a minute, then move the valve to the
pause position for about 5 seconds, then close the valve completely This removes
that trapped air around the isolation valve You will still see a rise in pressure, but
not as rapid The readings will start to stabilize the longer this hook-up is allowed
to vacuum down and use the pause position of the isolation valve the slower and
lower the rise in pressure
If you increase the volume of the cylinder and follow the same procedure, you will
notice a slower and lower rise If you watch your compound gauge, you will notice
there is no movement
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6

DIGITAL MICRON GAUGES

Inaccurate Readings

NOTE: For the JB digital vacuum gauges we have a stated accuracy that references
AVERAGE accuracy Thus, between 250 and 6000 microns the unit is +/-10%
AVERAGE accuracy and between 50 to 250 microns it is +/-15% AVERAGE
accuracy This does not mean our gauge has a large accuracy discrepancy
The term AVERAGE is an important part of this accuracy description The
number of increments displayed on the JB digital micron gauge between 50 and
250 microns are 97 Between 250 microns and 6000 microns, there are 232
increments If you take a comparison reading between the JB digital vacuum
gauges and the MKS Baratron master gauge at each of the increments displayed
on the digital micron gauge the average accuracy would be +/-10% in one range
and +/-15% the average in the other range Also, the number of increments
decrease from the lower micron readings to the higher micron readings
For example, from 250 to 300 microns there are 16 increments, from 650-700
microns there are only 7 increments, between 1000 and 1050 there are
4 increments, and between 4000 and 4500 there are 4 increments So at 650
to 700 microns the gauge has the ability to show 650-658-667-675-680-685-690-
695 But at the micron range of 4000 to 4500, the gauge only displays 4125-
4250-4375 This is important because when the system has an actual micron
level of 4260, the digital micron gauge will show a reading of 4375 because the
threshold for the lower value that the gauge displays, 4250, has not been reached
Once that threshold has been reached, the gauge will display that lower value of
4250 Because the readings in these higher micron ranges only need to show the
movement through them , the difference between 4375 and 4250 is of no concern
in reaching the ultimate vacuum desired This is why the JB digital vacuum gauges
are designed with the most increments in range that are going to be the most
critical in determining if the system is ready for charging
If you understand the size of a micron, then small differences in ranges is nothing
to be concerned about (Figure 16)
MICRON RANGE
60-100
200-350
500-700
900-1500
2500-4000
Figure 16
When a JB digital vacuum gauge comes in for repair, it is compared to a secured
system set up with a N I S T traceable master gauge Usually starting around
(1) 60-100 microns, then (2) 200-350 microns, then (3) 500-700 microns, then
(4) 900-1000 microns These ranges of vacuum are the most common that people
work with to determine deep vacuum

Erratic Readings

There are three issues involved in the discussion of erratic readings One is the
understanding of the gauge' s displayed micron increments that was just discussed
The second involves the re-sampling period The third is the environment inside
the system being evacuated When JB digital vacuum gauges are turned on,
the display will show "JB" and the sensor will start to calculate the ambient
temperature
Once the gauge has finished calculating the ambient temperature, it will display
"OOOOOO" indicating over-range if it is not introduced to a vacuum level of
100,000 microns or less
There is also instability inside the system being evacuated Liquids (moisture) are
being turned into gases and molecules are moving at different rates of collision
with other molecules at different areas of the system at different times between the
high and low sides The deeper the vacuum, the further apart these molecules get
MICRON DIFFERENCE
10-20
30-40
50-60
80-100
200-300