Regarding the HS-1 compared to the L4-C:

The HS-1 is a much larger sensor, about 4" in diameter, whereas the L4-C
is 2.75" in diameter and will fit inside 3" SCH40 ABS pipe for installing
it in a borehole. Installing the HS-1 in a borehole can be difficult if 
the steel outer case is not provided. 5" SCH40 ABS pipe is needed.

THe HS-1 has a period adjustment feature using an astitizing spring.
The L4-C period is not adjustable, and tends to get shorter with age,
a point to be considered in buying used ones. (have the period tested).
The period can be lengthened slightly be tilting the sensor up to 10 degrees.
Neither seis is easy to open up for adjustment, since any abuse of the
circular leaf springs will result in an unrecoverable loss of the longer
period and a trip back to the factory.

Electrically they can be equivalent if the coils are similar. THey both
have a 1kg mass and an intrinsic damping (Beta0) of around 0.27..

The cable on the L4-C connects to a 5 or 4-pin (w. or wout. cal coil)
Bendix connector in the top of the case. THe $75 cable mignt be the 
"geosensor" cable with the shovel-and-rodent-resistant thick resilient 
outer jacket. Belden instrumentation cable or shielded phono cable will do.
THe original cable is moulded into the top of the shell so that direct
installation under water is possible.

Most coil resistances for either seis are in the 1200 to 5500 ohm range.
I have been searching for one with a galvanometer impedance, less than
300 ohms, to use as a fedback instrument where the high resistances
will not work.

Regards,
Sean-Thomas

_____________________________________________________________________

Public Seismic Network Mailing List (PSN-L)