Specifications - City of Montpelier, Vermont

Montpelier District HeatingCity of Montpelier, VTIssue Date:September 28, 2012Title:15900 – Direct Digital Control SystemPage #:24 of 40The output ID 420 MA or 010 VDC current compatible withcontroller.F. Status and Safety Switches1. Current Sensing Switchesa. Current sensing switch shall be selfpowered with solid state circuitryand a dry contact output. It shall consist of a current transformer, a solidstate current sensing circuit, adjustable trip point, solid state switch,SPDT relay and an LED indicating the on or off status. A conductor ofthe load shall be passed through the window of the device. It shallaccept over current up to twice its trip point range.2. Low Temperature Limit Switchesa. The low temperature limit switch shall be of the manual reset type withDouble Pole/Single Throw. Snap acting contacts shall be rated for 16amps at 120VAC.b. The sensing element shall be a minimum of 15 feet in length and shallreact to the coldest 18 inch section. Mount element horizontally acrossduct in accordance with manufacturers recommended installationprocedures.c. For large duct areas where the sensing element does not provide fullcoverage of the air stream, provide additional switches as required toprovide full protection of the air stream.G. Temperature Sensors1. General Requirementsa. Input/output sensors and devices shall be closely matched to therequirements of the remote panel for accurate, responsive, noisefreesignal input/output. Control input response shall be high sensitivity andmatched to the loop gain requirements for precise and responsivecontrol.b. Temperature sensors shall be Resistance Temperature Detector (RTD)type of 100, 1000, or 3,000 ohm platinum, 500 ohm Balco, or 20,000ohm.c. The following shall apply to temperature sensors:1.) Stem or tip sensitive types.2.) Sensing elements shall be hermetically sealed.3.) Stem and tip construction shall be 304 stainless steel, copper,glass, or epoxy.4.) External trim material shall be corrosion resistant designed forthe intended application.2. Room Temperature Sensorsa. Room sensors shall be constructed for surface mounting.b. Room sensors shall have the following options:DIRECT DIGITAL CONTROL SYSTEMS1597224