ENDEVCO 2680M1, Instruction Manual

Page: 7 / 26

ENDEVCO
www.endevco.com Tel: +1 (866) ENDEVCO [+1 (866) 363-3826]
IM 2680/5 083119
7
04 INSTALLATION
The charge amplifier’s case is drilled with two holes for mounting the unit
to the test specimen. The mounting holes are drilled and counter bored
to accommodate a 6-32 cap screw. Since there are some measurement
difference between the 2680 and 2685, the user should refer to figures 12
A and 12B for measurement information. The mounting hardware for both
airborne amplifier models is listed in Table 4.
Quantity Description Endevco part
number
Mfg. part
number
1 Mating plug EP38 VP5/4CE6
1 Hood EP35 VS4/16C5
1 Potting sleeve EP31 VS4/16C9
1 6-32 ¼”cap screw,
CRES
EH535
1 6-32 ¾” cap screw,
CRES
EH293
To minimize noise pickup, the case of the charge amplifier should be
grounded to frame ground through the mounting screws, which act as
grounding lugs. Frame ground is then connected to circuit ground at
some single point to prevent ground loops.
04.1 Input Installation
This section covers the connections between the transducer and the
airborne amplifiers.
04.1.1 2680 input cable
The 2680 airborne amplifier is configured to operate with charge-mode
transducers thus the input cable must be low-noise treated. Cable
assemblies such as the Endevco 3090C or the premium 3090DV are
recommended. The connector on the airborne amplifier is a 10-32 type.
04.1.1.2 Input cable length
Since the 2680 amplifier supports high impedance charge-mode
accelerometers, it is important that the cable be as short as possible.
While cable length has no practical effect on sensitivity the high
impedance characteristics make the system susceptible to noise pick-up.
The model 2680 has an input source capacitance of 10 000 pF, maximum.
Thus the capacitance of the accelerometer plus the cable’s capacitance
must not exceed 10 000pf.
For example, using an Endevco 2276 piezoelectric accelerometer over
a distance of 80 feet (24 meters) between the accelerometer and the
airborne amplifier. The coaxial cable between the accelerometer and
Table 4 listing standard
accessories’ supplied.
The mfg. part numbers
refer to Viking
Electronics.