to control unit links which are within IDS protected area.
Circuit shall be supervised by monitoring changes in the current
that flows through the detection circuit and a terminating
resistor of at least 2.2 kohms. Supervision circuitry shall
initiate an alarm in response to opening, closing, shorting, or
grounding of conductors by employing Class C, standard line
security. Class C circuit supervisor units shall provide an alarm
response in the annunciator in not more than one second as a
result of the following changes in normal transmission line
current:
(1) Five percent or more in normal line signal when it consists
of direct current from 0.5 through 30 milliamperes.
(2) Ten percent or more in normal line signal when it consists of
direct current from 10 microamperes to 0.5 milliampere.
(3) Five percent or more of an element or elements of a complex
signal upon which security integrity of the system is dependent.
This tolerance will be applied for frequencies up to 100 Hz.
(4) Fifteen percent or more of an element or elements of a
complex signal upon which the security integrity of the system is
dependent. This tolerance will be applicable for all frequencies
above 100 Hz.
b.
Hardwire alternating current supervision: Supervision shall not
be capable of compromise by use of resistance, voltage, or current
substitution techniques. The method shall be employed on circuits
which employ a tone modulated frequency-shift keying (FSK),
interrogate-and-reply communications method. Supervisory circuit
shall be immune to transmission line noise, crosstalk, and
transients. Detection circuit shall be terminated by a complex
impedance. Supervision of the line shall be maintained by
monitoring current amplitude and phase. Complex impedance shall
be sized so that current leads or lags the driving voltage by
0.785 plus or minus 0.087 rad 45 plus or minus 5 degrees. For
supervision currents of 0.5 to 30 milliamperes root mean square
(rms), an alarm shall result when rms current changes by more than
5 percent, or phase changes by more than 0.087 rad 5 degrees. For
lines with supervision currents of 0.01 to 0.5 milliampere, an
alarm shall result when rms current changes by more than 10
percent, or phase changes by more than 0.139 rad 8 degrees.
Identified line supervision alarm shall be communicated within one
second of the alarm condition.
c.
Hardwire digital supervision: Modems at both ends of circuit
shall exchange digital data to indicate secure or alarm condition
at least every 2 seconds. For passive supervisory circuits, an
alarm shall sound if data is missed for more than one second.
Coding used for data shall not be decipherable by merely viewing
data on an oscilloscope. For transponder schemes, supervisory
circuit shall asynchronously transmit bursts of digital data.
Data pattern shall be random in nature. Remote detectors shall
receive data and encode a response based on a proprietary coding
scheme. Each IDS shall have a unique encoding scheme; an
industry-wide or vendor standard is not acceptable. Encoded
response shall be transmitted back to supervisory circuit.
Supervisory circuit shall compare the response to an anticipated
SECTION 13703N
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