HD
Fixed-temperature heat detector plan symbol
Fire alarm plan symbol for a fixed-temperature heat detector that alarms at a set temperature.
IEC
IEC · HD-R
Rate-of-rise heat detector plan symbol
Fire alarm plan symbol for a heat detector that alarms on a rapid temperature increase as well as a threshold.
In plain English
What does Rate-of-rise heat detector plan mean?
Rate-of-rise heat detectors alarm when temperature climbs faster than a set rate, and usually also at a fixed threshold. Plans use the heat detector form with an added rising mark or an R tag to distinguish it.
A simple example
They respond faster than fixed-temperature detectors to fast-growing fires, but can false alarm where temperature normally changes quickly, such as near ovens or doors to outside in winter. The plan location should be checked with this in mind. The symbol does not state the rate or threshold, which belong to the product class.
What the drawings help you do
Look for the rising mark or R tag. Check for rapid ambient changes near the location. A fixed-temperature detector waits for an absolute threshold; rate-of-rise reacts to the speed of change.
This particular reference
Fire alarm plan symbol for a heat detector that alarms on a rapid temperature increase as well as a threshold. A fixed-temperature detector waits for an absolute threshold; rate-of-rise reacts to the speed of change.
- Schematic
- A drawing showing function and connections rather than physical appearance.
Read the source: IEC graphical symbols for diagrams
IEC · Heat detector, rate of rise
IEC 60617 installation-plan style (architectural and topographical installation symbols); independently drawn, not certified IEC geometry or a database identifier.
Shown as an independently authored educational illustration. Use the cited publication and drawing legend to verify the required drafting form.
GA · HD-R
What it represents
Rate-of-rise heat detectors alarm when temperature climbs faster than a set rate, and usually also at a fixed threshold. Plans use the heat detector form with an added rising mark or an R tag to distinguish it.
They respond faster than fixed-temperature detectors to fast-growing fires, but can false alarm where temperature normally changes quickly, such as near ovens or doors to outside in winter. The plan location should be checked with this in mind. The symbol does not state the rate or threshold, which belong to the product class.
How to read it
- Look for the rising mark or R tag.
- Check for rapid ambient changes near the location.
Information to show or reference
- State class.
- Tag loop and address.
- Avoid locations with rapid normal temperature swings.
A distinction that matters
A fixed-temperature detector waits for an absolute threshold; rate-of-rise reacts to the speed of change.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
IEC graphical symbols for diagrams
IEC graphical symbol context for installation plans; independently drawn here.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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