In a message dated 30/04/01, karlc@.......... writes:

> Dr. Hutt told me this morning that they have one technical manual, and it 
> is about 500 pages.   

> Also, does anyone know if the helium pressure inside each individual sensor 
> might have been used to center the mass within its range? 

Hi there Karl,

>>Do changes in the gas pressure with temperature inside the sealed sensors 
units compensate for expansion or changes in spring constants? 

[Dennis Recla] 
No, the sensor is internally compensated so that there are no changes. Once 
stable in a bore hole, there isn't much temperature change. 


> nside each sensor canister is the capacitive detector, and electronics to 
> provide an output which connects to the other internal amplifier 
> electronics that connects via the downhole cable. The canisters can be 
> opened, by heating the brass cups and pulling the cup from the top plate, 
> all are made from brass (at least the early ones were) and soldered cup to 
> top plate. Each one is about 4 inch in diameter and about 6 inch long. 

>>      I would be very hesitant indeed before trying to open one. The 
electronics is actually inside the sensor cans? 

[Dennis Recla] 
Yes, the compenstation circuits and the capacitive to voltage electronics are 
inside each canister. 

       So, it looks as if the oscillator/demodulator signal conditioning 
circuits are inside the sealed sensor cans as might be expected. I presume 
that the electronics boards shown at the top of the main tube are the summing 
circuitry, output amplifiers, levelling controls and the power supply 
converters. It looks as if each sensor is hung on a spherical mounting which 
can be supplied with compressed air from the small pump to make it levitate, 
which levels the sensor.

       Remembering that these units may be 30 years old and the transistors 
may have been rated for a 10 year life (we tend to forget that valves had a 
42 day rated life), it is possible that there could be some which are now a 
bit noisy as well as being of obsolete type. I wonder now if the USGS has any 
unwanted spare parts lying around....?

       Hope that this helps,

       Chris Chapman
In a message dated 30/04/01, karlc@.......... writes:



Dr. Hu
tt told me this morning that they have one technical manual, and it 

is about 500 pages.   





Also, does anyone know if the helium pressure inside ea
ch individual sensor 

might have been used to center the mass within its range? 




Hi there Karl,



>>Do changes in the gas pressure with t
emperature inside the sealed sensors 

units compensate for expansion or changes in spring constants? 



[Dennis Recla] 

No, the sensor is internally compensated so t
hat there are no changes. Once 

stable in a bore hole, there isn't much temperature change. 





I
nside
 each sensor canister is the capacitive detector, and electronics to 

provide an output which connects to the other internal amplifier 

electronics that connects via the downhole cable. The canisters can be 

opened, by heating the brass cups and pulling the cup from the top plate, 

all are made from brass (at least the early ones were) and soldered cup to 

top plate. Each one is about 4 inch in diameter and about 6 inch long. 




>>      I woul
d be very hesitant indeed before trying to open one. The 

electronics is actually inside the sensor cans? 



[Dennis Recla] 

Yes, the compenstation circuits and the capac
itive to voltage electronics are 

inside each canister. 



       So, it looks as if the oscillator/demodulator signal conditioning 

circuits are inside the sealed sensor cans as might be expected. I presume 

that the electronics boards shown at the top of the main tube are the summing 

circuitry, output amplifiers, levelling controls and the power supply 

converters. It looks as if each sensor is hung on a spherical mounting which 

can be supplied with compressed air from the small pump to make it levitate, 

which levels the sensor.



       Remembering that these units may be 30 years old and the transistors 

may have been rated for a 10 year life (we tend to forget that valves had a 

42 day rated life), it is possible that there could be some which are now a 

bit noisy as well as being of obsolete type. I wonder now if the USGS has any 

unwanted spare parts lying around....?



       Hope that this helps,



       Chris Chapman