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TM 11-6625-3023-14/ET904-AA/MMA-010/E154 TS3684/TO 33A1-12-1173-1
CHAPTER 4
FUNCTIONAL DESCRIPTION
4-1.
Introduction. This chapter provides the functional description of the test set. A brief description of the electric
surge arrestors (ESA) devices is presented first, followed by a general overall functional and detailed circuit description
of the test set.
4-2. Signal ESA Theory. The TS-3684/T Test Set is capable of checking three different types of ESA devices: bulk
devices and those associated with coaxial (digital transmission) lines, intercom and EOW lines. The ESA devices
conduct whenever the voltage across them exceeds a particular threshold (ionization potential).  Each individual
transmission wire has an ESA device connected between it and earth ground at the point-of-entry to the equipment.
Prior to conducting, the ESA device exhibits a high impedance which is negligible to a transmission system. During
conduction the device has a very low impedance and therefore shunts the surge energy to ground, thereby limiting the
stress to subsequent electronic components. A brief description of the three types of ESA devices is as follows:
a.
Bulk
- All conductors are protected by a common gas (tritum)
chamber which ionizes and shunts all the conductors if
the threshold voltages (350 Volts, nominal) are
exceeded on any signal conductor.
b.
Coaxial intercom
- Conductors are protected by individual
and end of wire
button-like gas filled devices built into
(EOW) lines
a high voltage assembly. These devices
have a 90-Volt nominal threshold voltage.
4-3.
Test Set Functional Description (fig. FO-2).
a.  General. The test set consists of a transformer-coupled, voltage-doubler, current-limited regulated power
supply capable of operating from a power source of 105 to 130 VAC of either 50, 60 or 400 Hz. Switches are provided
for device selection (bulk, coax or external EOW), type of test (SHORT or OPEN), and TIP-RING selection, in addition to
two momentary toggle switches to initiate testing.
The SHORT test consists of placing an incandescent lamp in parallel with the ESA device being tested. If the
arrestor is good (not excessively leaky or shorted), all the available current will flow through the lamp, causing it to light.
If the arrestor is shorted or has an abnormally low impedance, the lamp will not be able to light because most of the
current will flow through the arrestor.
The OPEN test consists of placing the incandescent lamp in series with the ESA device being tested. If the
arrestor is good (has an ionization threshold below the applied test voltage), it will ionize, and the current that flows will
light the lamp, giving a green indication. If the arrestor is open or has a breakdown threshold
4-1

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