Fluid Components International FLT93 Nuclear - Manual (Page 7)

FLT ® Series FlexSwitch TM GENERAL
Fluid Components International LLC 7
1 GENERAL
Description
The FLT Series models are multipurpose measurement instruments. The FLT Series models that are included in this manual are FLT93-S, FLT93-F,
FLT93-HT and FLT93-L. Each model is a single instrument that is capable of detecting fl uid fl ow and temperature. It is also able to detect liquid level
or fl uid media interfaces. The instrument has two fi eld adjustable alarm set points, two buffered voltage outputs, as well as a built-in calibration
circuit. The output of the alarm set points are 6 amp relay contacts that can be used to control customer process applications. An optional 10 amp
relay contacts can be used to control the customer process application. One buffered voltage output is available for fl ow or level monitoring and the
second buffered voltage output is available for temperature monitoring.
Theory of Operation
The fl ow switch is a fi xed position, single-point fl ow, level, interface and temperature switch. The operation of the sensing element is based upon
the thermal dispersion principle: A low-powered heater is used to produce a temperature differential between two Resistance Temperature Detec-
tors (RTDs). The RTD temperature differential varies as a function of forced convection for fl ow measurement and as a function of fl uid thermal
conductivity for level and interface measurement. The measurement of the fl uid’s temperature is obtained from the non-heated RTD.
Sensing Element
The sensing element consists of two thermowells (hollow tubes) that when inserted into the fl ow process allows an unimpeded fl ow inside the
process line. The top thermowell has a self-heated RTD inserted into it. The bottom thermowell has a reference RTD inserted into it. In order to
correctly orient the sensing element a fl ow arrow has been etched onto the threaded portion of the sensing element. See Figure 1-1 for a view of the
sensing element.
Control Circuit
The control circuit converts the sensing element’s RTD temperature differential into an analog DC voltage signal. Dual comparators monitor the
sensing element signal and activates the relay alarm circuits if the signal exceeds an adjustable set point.
The control circuit contains fi eld removable jumpers that confi gures the instrument to perform in the fi eld as needed by the customer.
Figure 1-1 View of the Sensing Element