Humidistat Accuracy (long)

[Roger Wheelock]

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Hello List,

Bob Mair, CEO of Dampp-Chaser Corp., has asked me to post the following =
related to the recent thread on humidistat accuracy.

Thanks!

Roger

Don Rose has hit the nail right on the head in his 12/01/02 response to =
Terry.

Stand alone Dehumidifiers normally are rated in amps and those that we =
routinely use are 6.3 amps and 7.5 amps. I don't think they go much =
higher. I have seen 5.3 amp units and may have at some point in the =
distant past seen 3.9 amp units.

If you want to convert amps to watts you can use the rough rule of thumb =
that 1 amp equals 120 watts. Again, more for information than anything =
else, Dampp-Chaser Humidistats are rated at 200 watts max for the =
Dehumidifier side, 20 watts for the Humidifier side. They contain =
essentially the same switch that was used years ago, so they are capable =
of withstanding an overload. However, they are not designed to control a =
Dehumidifier rated at 6.3 amps steady state that draws 6 times that =
during start up. Particularly when start up can occur a number of times =
each day in a piano application.

On hygrometers, Klaus Fenner wrote an article for the Piano Technicians =
Journal, sometime in the late 1980's, describing what all manufacturers =
of "hair" hygrometers know, and for the most part are willing to =
acknowledge. After operating in the same RH level for a substantial =
period of time they get "lazy" and won't move out of this level even =
when the RH level demands that they do so. They require "exercising" to =
bring them back to proper operation. Lufft hygrometers are sold with =
instructions on exercising. They call it recalibration but it, in fact, =
is exercising. Be careful when using your "hair" hygrometer that it has =
not become lazy. If anyone is interested in the Klaus Fenner article, =
let me know and I'll make you a copy.

I believe our promotional literature describes our System as maintaining =
an AVERAGE RH level of 42%, not a maximum 42%. On this subject, does =
anyone read our Newsletter? We sent 15,000 Newsletters out this past =
June that contained an article on Humidistat testing. It had 2 great =
pictures showing Humidistat switch testing and some very good =
explanation. The following is a portion of the article:

Creates its own Environment

How the Humidistat switch works: The electromechanical switch has a =
polymer band which swells as the relative humidity rises and shrinks =
when the relative humidity falls. During testing, computers monitor and =
register the set points at which each switch changes from the =
humidifying to the dehumidifying mode. Our specifications regarding set =
points: the high event must be no higher than 51.5%, the low event no =
lower than 39.0% with a differential no greater 8%.

04502-C0425 57

Time degF %R Evnt

1510 81.3 57.8 High

2044 81.0 42.1 Low

0437 81.3 48.3 High

Above, an actual switch test record. This is a recording of the action =
of each switch which is made during a 16 hour test period. The "042502" =
on the record is April 25, 2002 (the date of testing is on all =
Humidistats). Throughout the test, the temperature fluctuated between =
81.0F and 81.3F. As the test began, the relative humidity was 57.8%. To =
test the switch in the Humidification mode, the RH was lowered, and at =
42.1%, this switch energized the Humidifier. In our terminology, 42.1% =
is the lower set point. The chamber then automatically began raising the =
humidity to simulate the conditions in a piano when the Humidifier is =
operating. As humidity increased, the polymer band swelled until an =
upper set point of 48.3% relative humidity was reached. At that point, =
the switch energized the Dehumidifier and shut off the Humidifier. The =
switch in the table above had a differential of 6.2%, which is well =
within our standards. The narrow differential produces a narrow range of =
relative humidity which forces the soundboard to stabilize at a constant =
moisture content, regardless of room humidity levels. In this way, the =
System creates its own environment within the piano.

Now perhaps the most important part of this message is: We have a great =
technical support section at Dampp-Chaser and are happy to help any and =
all. It's far more beneficial (and easier) to talk about a Technicians =
specific problem over the phone than it is by way of email. If something =
isn't going right or you think it's not going right, call us. That is =
why we are here. The number is 1-800-438-1524. Ask for Bob, Mitch or =
Roger.


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