ProMelt Snow Melting PM-824 Detector

ProMelt Snow Melting PM-824 Detector

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PM 824 Rain amd Snow Sensor Controller

The PM-824 is an advanced low voltage version of the DS-8. It is primarily designed for hydronic and low voltage gutter, downspout, and roof ice melting applications. It can also be used on existing buildings where retrofitting high voltage wiring would be to difficult. The 24VAC/VDC supply means less expensive wiring, no requirement for conduit, and lower installation costs

  • Designed for Low Voltage Hydronic and Battery Powered Systems
  • Automatic Activation means Lower Deicing Costs
  • Reliable Rain and Snow Detection
  • 24VAC/VDC Operation, Only 20 VA Required
  • Full 30A @ 24VAC Control
  • Replaceable Remote Precipitation Sensor
  • Easy Installation, Full Access to Electronics
  • 8 Different Functions, 1 Part Number
  • Adjustable Temperature Trigger Point
  • Adjustable Delay Off Cycle, Selectable 30-90 Minutes or 2-6 Hrs
  • Exclusive Adjustable Sensitivity Control
  • Selectable Low Temperature Cutoff
  • Smart "Manual On" Operates for One Delay Off Cycle
  • High Power, Low Price!

The unit is housed in a two gang PVC enclosure. The overall dimensions of the PM-824 are 4¾"(120) x 7"(178) x 2¾"(70). The unit weighs 2 pounds. The user may access all electronics by removing the four front cover screws. The remote precipitation sensor includes 10 feet (3 m) of interconnect cable. A weatherproof LED indicator on the base of the unit provides a method of checking power and trigger status when the unit is mounted in a "hard to reach" location. Steady OFF indicates no power to the unit. Steady ON indicates power is being supplied but no snow or rain trigger is active. A blinking LED indicates the DS-824 is triggered and connected equipment has been activated.

Wiring is performed by terminating your existing wiring to the pre-installed pigtails. The DS-824 is mounted by either attaching the mounting hub to a rigid ½" or ¾" conduit or by installing screws through the four mounting tabs provided.

The PM-824 can be powered from a 22-28VAC/VDC source. Peak power consumption is 15 VA at startup, 8.5 VA steady state triggered, 5 VA steady state un triggered. Power input is polarity protected for a DC supply. The unit provides a single 24VAC/30A or 24VDC/20A normally open load contact set. This contact set is paralleled with a low power contact set to provide remote control and activation monitoring. Operational temperature range is -40oC to +85oC.

The table below outlines the operating modes for the PM-824. Trigger Temperature (TT) is adjustable from 34oF-44oF using an on-board control. When ambient air temperature (AT) is below this trigger point precipitation is assumed to be snow or freezing rain. When above the trigger point, precipitation is assumed to be rain.

"Delay Off" refers to the internal drying cycle timer of the PM-824. The timer is used to allow the PM-824 to dry the heated surface through evaporation once precipitation has stopped. The drying cycle reduces the chance that moisture left behind by the melting process will refreeze into ice. This timer is restarted by each precipitation detection. Therefore, the PM-824 will continue to operate as long as precipitation and trigger temperature is detected, then for the "Delay Off" time once rain or snow stops. It is assumed that, when operating as a sensor, the PM-824 is supplying an activation signal to an external control system. All "sensor" modes provide a minimum 2 minute closure, reducing cycling of the external controller. The Delay Off cycle has been extended for hydronic applications and is determined by the Long Delay (LD) switch setting, DEL switch setting and the DEL adjustment. Delay Off is 30-90 minutes in non-LD "controller" mode and 2-6 hours in LD "controller" mode.

An environmentally sealed control switch is provided. The "Manual On" function activates the controlled equipment for testing and special operational conditions. The "Automatic" position allows the PM-824 to handle all detections and control. The "Standby/Reset" position disables triggering and can also be used to clear the delay off timer (see below) from true or test activation. If the switch is placed in "Manual On" for less than 2 seconds, then switched back to "Automatic" the controller will execute one delay off cycle. This allows a controlled manual activation of the snow melt system without the fear of forgetting and leaving the system in "Manual On" for an extended and potentially very expensive period of time. "Standby/Reset" can still be used to clear this delay off cycle. Remote control and monitor up to 1000 feet away is also available when the optional CS-1 C/M cable listed is installed. The PM-824 is also compatible with the DP-7B, DP-7EX, and CDP-2 remote control/status panels.

The Low Temperature Cutoff (LTC) option is typically used on deicing or snow melting systems with limited output capacity. If selected, the sensor will not trigger if precipitation is detected below 15oF. However, if the deicing system has been activated, precipitation continues, and the ambient temperature drops below 15oF, LTC will be ignored. This assures that water left behind on the surface during the heating cycle will not immediately refreeze into ice as a result of deactivating the deicing system.

The PM-824 also features a new innovation, a Trigger Sensitivity Adjustment. Previous units have always detected and triggered on the first drop of rain, the first flake of snow. While this has always provided a highly reliable detection it may create "nuisance" triggers in some installations. Snow blowing off a roof or falling from a tree could cause the system to activate for a delay cycle when its not needed, increasing operating costs. The sensitivity adjustment allows setting the number of seconds the precipitation grid must see continuous rain or snow before the sensor is triggered and ranges from 3 seconds to 4 minutes. A higher sensitivity setting assures quick detection no matter the conditions. A lower sensitivity setting will allow a few stray drips of rain or flakes of snow to be ignored but a heavier downfall will trigger the system.

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ProMelt PM-824 Spec & Installation Guide

SunTouch 25 years Warranty


  • Model: 81011696


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