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Therefore, it is ideal for gas lasers where
the gases are almost never just plain old air!
But for many applications (some of ours included), they may more than outweigh the fast response, superb accuracy
and resolution, and gas independence of capacitance manometers.
As you will read below you shall find useful tips on how you may find
a repairer in your locality, what to expect and what
to avoid. Thus, if you find an older model, realize that it may have its own set of quirks that
will need to be dealt with to maintain your sanity. It will be a simple matter to restore if I find an actual problem elsewhere.
If the pump results in pressure pulsations, these
will even be detectable on a readout with sufficiently fast response.
The response time is almost instantaneous compared to a TC
gauge - typically 5 ms rather than many seconds or minutes.
To take advantage of the fast response of the capacitance manometer gauge, an analog meter is really much better than a digital display.
The long (but normal) warmup time is the most significant annoyance with the 227A.
Cycling between 1 atm and high vacuum doesn't result in much of a change in the zero setting - perhaps 1 or
2 microns at most.
Cycling between a pressure within the specified range and 1 atm or above may require re-zeroing
of the transducer due to mechanical stress.
At times you may be able to clear the error and
restart the cycle. WARNING: Unlike thermocouple gauges with their mostly low voltages,
ionization gauges may have 150 V to 800 V or more with enough current available to be lethal inside the unit
as well as on the various electrodes of the ion gauge tube sensor.
Every one of the things that you will require like
drain or natural product will be inside eye level. Slide the scale so that the zero line aligns with the fluid level.
I made some measurements of a few internal signals including the 10 V and 1.9 V references, the oscillator frequency from the manometer, the output voltage after the frequency-to-voltage converter, and
the zero voltage reference (the 1.9 V reference multiplied by a bit over 5, adjustable via the
Zero pot). Unfortunately, the basic design of this system results in the
output for zero microns being derived from the difference of two large numbers so small changes in either have a
large effect.
Without specifications for the capacitance of the diaphragm and/or frequency calibration, all
I could check out was the electronics and as far as I could tell, this was
operating correctly, including the gain (span) and zero circuitry,
and temperature regulating heater. It is essential to check that your local plumbing professional has all the necessary knowledge
needed to practice their trade. It is important to check
the warranty associated with your special refrigeration unit before purchasing it because a durable fridge is a long-time purchase.
All that will definitely change in the future because
of their extended warranty which I have only need ONCE and while I got a service date
they said I wasn't under warranty which I AM. Because dishwasher
parts break down and need replacement over time,
it’s necessary to be sure to stay on top of your dishwasher’s maintenance.
I have been told that I need to replace the entire oven, but
I do not believe this.
A frequency-to-voltage converter (basically a triggered pulse generator and averager) followed by op-amp
circuits to adjust gain (span) and zero setting provides an output voltage (typically) between 0 and 10 VDC
where 10 VDC corresponds to full scale with extremely good linearity with respect
to pressure over the entire range. As noted, the output is just a voltage which is
linear with respect to pressure over its specified range.
A gauge of this type would be ideal for the HeNe and Ar/Kr ion lasers, and others that are pumped down and maintained below a certain pressure over long periods of operation or prior to
seal-off of the tube. The diaphragm is somewhat flexible acting as a nearly ideal spring over a range of pressures determined by the
mechanical design of the tansducer. For a vacuum sensor, a thin metal diaphragm separates
a permanently evacuated and sealed "reference" volume from the vacuum
system whose pressure is being measured. Possibly the diaphragm had been damaged from mechanical
shock or sudden pressure changes. At any given instant, the sensor will respond to pressure changes accurately
but the zero setting will continue to drift during the warmup period.
Now, it can be zeroed at any time but the zero setting
drifts by about 30 microns from a cold start to an hour or
so later.
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