Section I. GENERAL
This technical manual contains a general description with equipment parts list, installation information, operating
instructions, description of equipment operation, crew/operator maintenance information, organizational maintenance
information, direct support (intermediate) maintenance information, three appendixes, a schematic for the Capacitance
Proximity Sensor DT-548( )/FSS-9(V) and an index.
1-2. Maintenance Forms and Records
Department of the Army forms and procedures used for equipment maintenance will be those prescribed by TM 38-750.
1-3. Reporting of Errors
The reporting of errors, omissions and recommendations for improving this publication by the individual user is
encouraged. Reports from U. S. Army users should be submitted on DA Form 2028 (Recommended Changes to
Publications) and forwarded direct to Commander, U. S. Army Troop Support Command, ATTN: AMSTS-MPP, 4300
Goodfellow Boulevard, St. Louis, MO 63120. Reports from U. S. Air Force users should be submitted on AFTO Form 22
and forwarded to HQ, SAAMA/MMSTR Kelly AFB, Texas 78241. Reports from U. S. Navy users should be submitted on
Technical Manual User Activity Comment Sheet and forwarded to Naval Elect Systems Command, National Center
Building 1, ATTN: ELEX-4903, Washington, D.C. 20360.
Section II. DESCRIPTION AND DATA
1-4. Purpose and Use
The Capacitance Proximity Sensor (fig. 1-1), hereinafter referred to as the CPS, is an electronic security device used to
protect such items as file cabinets, safes, and desks when connected into the FSS-9 security system. The sensor works
with a Control Unit, C-9412, and any one of three Monitor Units CY-7359, CY-7360 or CY-7361.
The CPS detects human bodies or hands approaching to within one inch of a protected metal object and generates an
alarm signal when detection criteria are met. The CPS senses a change in capacitance to ground of the protected metal
object (which must be insulated from ground) resulting from a change in the nature of the air dielectric between the metal
object and ground. Such change in dielectric results when a human body approaches the metal object The rate of
change of capacitance (dc/dt) must be within certain values for an alarm to be generated; therefore, slow changes such
as result from humidity, settling dust, etc., do not generate an alarm signal, nor do fast disturbances resulting from
a. Equipment Protection and Alarm Conditions. The extent of security afforded by the CPS can only be defined in
terms of the inherent capacitance of the object(s) to be protected. The CPS can protect up to 15, 000 picofarads of
equipment (capacitance with respect to ground of the equipment) when the equipment is properly insulated from ground
and interconnected with the cable furnished as part of the system. One or two relatively large objects or several smaller
ones exhibit approximately 15, 000 picofarads capacitance to ground (refer to para 2-8 for examples). The CPS also
protects itself, generating an alarm if the control cable is cut or shortcircuited, if the container is opened without
authorization, or if power to it fails.
b. Alarm Operation. The CPS has two switch selected levels of sensitivity. The HI sensitivity position protects up
to 5, 000 picofarads of equipment and alarms on a change of ±14 picofarads or more; the LO sensitivity position protects
up to 15, 000 picofarads of equipment and alarms on a change of ±42 picofarads or more. However, at either setting the
alarming capacitance change must occur in not longer than 20 seconds nor shorter than 1/10th second duration for an
alarm to be generated. The alarming capacitance change is from the static or stable capacitance of the protected array
of equipment, and no adjustment of the CPS is necessary to establish the baseline of stable capacitance. The alarm
signal from capacitance change and the alarm signal from tampering are available at separate terminals and are
independent. Therefore, if desired, the two types of alarms can be distinguished from each other.