Metrix 440 - Page 9

Doc# 90018-031 • REV L (April 2016) Page 9 of 16
5.3.1 LightLoads
The solid state triacs used in the standard 440 series are a special high transient immunity,
medium power type. O state leakage is 1 mA max and should not create any problems,
even when interfaced with a load as light as a programmable controller.
Minimum load required to keep the triac on is 20 mA typical and 50 mA max due to the
“holding current” specicaons. If the load is less than this, a resistor may have to be
placed in parallel with the load, i.e.; for 115 VAC light load (50 mA or less) a 2K-ohm 10
wa power resistor is recommended.
5.3.2 D.C.Loadswithtriacs
Although most applicaons use AC input power and AC on the triac outputs (alarm and
shutdown), these triacs may be used in DC applicaons providing minimum loading re-
quirements are met. When DC is used, a triac will automacally latch in the “on” condion
aer trip, thus only “close on alarm” (N.O.) can be used. To reset an external reset switch,
the rest switch must be wired in series with the load. To avoid large voltage drops during
DC operaon, the triac should be connected as follows:
Shutdown: Term 4 POS Alarm: Term 14 POS
Term 3 NEG Term 13 NEG
5.3.3 170mAAnalogSwitchOpon
The special condions of secons 5.3.1 and 5.3.2 do not apply. However, maximum cur-
rent is limited to 170 mA.
5.4 FunconalCircuitBlockDescripon
An internal transducer module consisng of a crystal assembly and integral charge amplier
senses vibraon. Thus, the electrical output of the transducer is a well-buered (low imped-
ance) signal directly proporonal to vibratory acceleraon levels (g) at the switch.
The raw acceleraon signal goes to a custom hybrid circuit that integrates the signal and pro-
vides an AC signal proporonal to vibratory velocity instead of acceleraon. This signal is then
routed through an amplier, the gain of which is controlled by the shutdown setpoint.
Next, the signal is processed through a true RMS-to-DC stage and compared against a preset
internal voltage reference. If the signal level is higher than reference, the shutdown LED is
illuminated.
If the voltage level stays above the reference for the duraon of the me delay, an output
trip occurs and the shutdown solid-state relay will trip.
Alarm trip is derived in much the same manner, branching from the output of the RMS-to-
DC stage. Likewise, the DC output is directed to the voltage-to-current hybrid.
NOTE: Models using an external (Ordering Opon I=5)
sensor do not have an internal accelerometer and will
measure vibraon at the sensor locaon, not the switch
locaon. Refer to Metrix product datasheet 1004730 for a list
of ordering opons characterizing external transducers.