Thermal fire sensor: types and connection diagrams


smoke and sensor

It is impos­si­ble to be pre­pared for a fire, it is always sud­den and uncon­trol­lable. But it is pos­si­ble to min­i­mize the risk of its occur­rence by sig­nif­i­cant­ly reduc­ing the pre­dictable mate­r­i­al dam­age. To do this, spe­cial­ists invent­ed fire detec­tors, which are cur­rent­ly the only means capa­ble of detect­ing a fire with­out a per­son. One of these of its kind is a ther­mal fire detec­tor or detec­tor, briefly — TPI.

The principle of operation of TPI and features of its design

The name itself — ther­mal — explains the prin­ci­ple of oper­a­tion of the device. It con­tains one or more trans­duc­ers — sen­si­tive ele­ments, which, per­ceiv­ing the tem­per­a­ture increase in the envi­ron­ment, lead to the oper­a­tion of a loud iden­ti­fi­ca­tion sig­nal through an audi­ble annun­ci­a­tor.white sensor on the ceiling

There is anoth­er type of detec­tor — fire smoke. It is trig­gered by aerosol com­bus­tion prod­ucts, in oth­er words, smoke, or rather, its col­or. The advan­tage of fire smoke detec­tors is that it is allowed in admin­is­tra­tive build­ings, unlike a heat detec­tor, and the minus is that it will raise every­one to their feet not because of a fire, but, for exam­ple, a large accu­mu­la­tion of dust or steam. More­over, strict­ly speak­ing, it is wrong to call it a sen­sor, because it is only an inte­gral part of the detec­tor.

Main types

locations and types

By the appear­ance of the main com­po­nent of the TPI — a sen­si­tive ele­ment or con­troller, there are four main types of it:

  • Con­tact TPI. When the tem­per­a­ture regime changes, the estab­lished con­tact or the elec­tri­cal cir­cuit opens, the spe­cial loop breaks and caus­es the sound sig­nal to sound. The sim­plest, as a rule, domes­tic mod­els, are a closed con­tact of two con­duc­tors, packed in a plas­tic con­tain­er. More com­plex ones have a tem­per­a­ture-sen­si­tive semi­con­duc­tor with neg­a­tive resis­tance. If the tem­per­a­ture mark of the envi­ron­ment increas­es, the resis­tance will drop, and a con­trolled cur­rent will flow through the cir­cuit. As soon as it reach­es a cer­tain indi­ca­tor, the alarm will work.
  • AT elec­tron­ic sen­sor mount­ed sen­sors that are inside the cable, as soon as the tem­per­a­ture reach­es a cer­tain thresh­old, the resis­tance of the elec­tric cur­rent in the cable changes, which is trans­ferred to the con­trol of the con­trol device. High­ly sen­si­tive. The prin­ci­ple of the device is quite com­pli­cat­ed.
  • Opti­cal detec­tor works on the basis of an opti­cal fiber cable. As the tem­per­a­ture ris­es, the opti­cal con­duc­tiv­i­ty changes, which leads to an audi­ble warn­ing.
  • Met­al tube with gas, her­met­i­cal­ly filled, required for mechan­i­cal TPI. The impact of tem­per­a­ture on any part of the tube will lead to a change in its inter­nal pres­sure and an alarm will be trig­gered. Declared obso­lete.
  • Oth­er types. Semi­con­duc­tor ones have a spe­cial coat­ing with a neg­a­tive tem­per­a­ture coef­fi­cient, electro­mechan­i­cal ones con­sist of wires under mechan­i­cal stress coat­ed with a tem­per­a­ture-sen­si­tive sub­stance.

Types of fire detectors

Ther­mal fire­fight­ers react to dif­fer­ent para­me­ters of the spread of fire. Hence the clas­si­fi­ca­tion into types.installer puts sensors in the office

The absolute val­ue thresh­old is set to the max­i­mum fire detec­tor:

  • pres­sure,
  • tem­per­a­ture — as soon as the envi­ron­men­tal indi­ca­tor reach­es it, peo­ple will be noti­fied.

Domes­tic devices are mass-pro­duced with a response tem­per­a­ture of 70–72 degrees. They are also very pop­u­lar because of their afford­abil­i­ty.

For a dif­fer­en­tial fire alarm sen­sor, the rate of change of the attribute that it con­trols is impor­tant.

Such devices are rec­og­nized as more effi­cient than the max­i­mum TPI -

  • give ear­ly warn­ing
  • sta­ble in oper­a­tion, but due to two ele­ments installed at a dis­tance, they are more expen­sive.

Max­i­mum dif­fer­en­tial instru­ments com­bine both para­me­ters.

If you are going to pur­chase this type of fire equip­ment, please note that their tem­per­a­ture thresh­old must be at least 20 degrees high­er than the per­mit­ted tem­per­a­ture at the facil­i­ty.

Thus, tech­ni­cal spe­cial­ists divide mod­ern fire alarm sys­tems into dis­crete (by thresh­old) — they are dis­cussed above — and ana­log. Ana­log ther­mal fire sen­sors, in turn, are divid­ed into con­ven­tion­al and address­able. The lat­ter trans­mit not only infor­ma­tion about the fire, but also the code of their address.

Both dis­crete and ana­log mea­sure the char­ac­ter­is­tics of fire fac­tors, the fun­da­men­tal dif­fer­ence is in the way the sig­nal is processed.

For ana­log ones, it is more com­pli­cat­ed and its essence is in spe­cial sys­tem­at­ic algo­rithms.

  • Address­able ana­log ther­mal devices reg­u­lar­ly col­lect infor­ma­tion about the state of the premis­es. They can give out the data they are pro­grammed to col­lect in real time.
  • Explo­sion-proof ther­mal fire detec­tors are need­ed where the risk of fire is high and explo­sive sub­stances may be present in the air. They seem to be armored, as they are locat­ed on var­i­ous pow­er units, oil pipelines, etc. They dif­fer in the degree of pro­tec­tion, the num­ber of sen­sors and the dif­fer­ent tem­per­a­ture thresh­olds set.
  • At lin­ear heat detec­tors a cable with a heat-sen­si­tive poly­mer is used — a ther­mal cable — it cap­tures any changes along its entire length as a sin­gle fire sen­sor. Used where the ceil­ing is large, such as an indoor sta­di­um. You can also mount on the walls in addi­tion to the ceil­ing.
  • Mul­ti-point ther­mal devices opposed to inher­ent­ly lin­ear. They are part of a sin­gle sys­tem that con­trols sev­er­al zones and is com­bined into an elec­tri­cal cir­cuit. The sig­nals com­ing from fire sen­sors are processed in a sin­gle unit.

Operation and installation

The con­nec­tion dia­gram for ther­mal sen­sors is giv­en in the instruc­tion man­u­al, how­ev­er, dif­fi­cul­ties may arise.

The require­ments of GOST R 53325–2009, para­graph, oblige to sup­ply heat detec­tors with a built-in or remote opti­cal indi­ca­tor.

When cal­cu­lat­ing the val­ues ​​of addi­tion­al resis­tors, take into account the elec­tri­cal com­po­nents of the con­nect­ed LED indi­ca­tors.

Look in the device data sheet for the typ­i­cal and max­i­mum volt­age drop, which indi­cate the lim­it of the para­me­ters. For ease of instal­la­tion, it is bet­ter to take LED non-polar indi­ca­tors.

Nor­mal­ly closed con­tacts of ther­mal devices are con­nect­ed to the loop in the same way as for smoke devices. The dif­fer­ence is that in the stand­by state, ther­mal sen­sors do not con­sume elec­tric cur­rent, and in active mode it is less than that of smoke sen­sors.

Ther­mal fire alarm sen­sors have the fol­low­ing resis­tances in the con­nec­tion dia­gram:

  • Rbal.,
  • Roc.,
  • Radd.

We study the instruc­tion man­u­al for the con­trol device and take into account the resis­tor val­ues.

Rbal. sim­i­lar to Radd., but it is not includ­ed in the con­trol device kit, you will have to buy it addi­tion­al­ly.

In nor­mal mode, the sen­sors are short-cir­cuit­ed, which means that the resis­tance Rbal will occur only if one or two of the devices work. And then the “Alarm” sig­nal can be formed.

For con­trollersMirage” is the fol­low­ing dia­gram. If one works, then the “Atten­tion” sig­nal will come in, if the sec­ond one, the “Fire” com­mand will fol­low.

The des­ig­na­tion of the heat detec­tor in the dia­gram, as well as oth­er com­po­nents, is as fol­lows:

  • ShS — alarm loop
  • IP — ther­mal fire detec­tor,
  • YPRES — man­u­al fire detec­tor
  • DIP — fire smoke detec­tor.

Con­di­tion­al graph­ic des­ig­na­tion of an auto­mat­ic heat detec­tor accord­ing to the require­ments of reg­u­la­to­ry doc­u­men­ta­tion — .

Norms and fea­tures of instal­la­tion / con­nec­tion of ther­mal sen­sors are reg­u­lat­ed withwater of the rules of the fire pro­tec­tion sys­tem with the lat­est changes from 20.06.2011

From table 13.5, the dis­tance between the ther­mal spot devices, as well as between them and the wall, becomes known (do not for­get about the excep­tions indi­cat­ed in para­graph 13.3.7).

Source: SP5.13.130.2009.

It is easy to guess that the area cov­ered by the sen­sor depends on the height of the room. At the same time, many install two devices in each room in case one sen­sor fails.

The dis­tance from one to the oth­er should be lim­it­ed to half the rec­om­mend­ed. But this works with point non-address sen­sors. Ana­log address­able ones do not need dupli­ca­tion, since they have a com­plete­ly dif­fer­ent prin­ci­ple of oper­a­tion.

  • When locat­ing sen­sors in rooms, it is nec­es­sary to take into account the pecu­liar­i­ties of the dis­tri­b­u­tion of com­bus­tion prod­ucts in them.
  • It is inef­fi­cient to install heat sen­sors in “dead” zones, where the hot air will reach the last place, and the fire extin­guish­er will work too late.
  • So, when lay­ing a ther­mal cable of a lin­ear heat detec­tor, it is not nec­es­sary to do this 15–20 cm from the cor­ners along the ceil­ing and walls.
  • Do not for­get about hoods, air con­di­tion­ers — place the device at least a meter away from them.

Phys­i­cal laws give rise to the prin­ci­ples that under­lie the instal­la­tion of fire detec­tors:

  • a flat ceil­ing is pro­tect­ed along a cir­cle lying in a hor­i­zon­tal sur­face;
  • you need to take into account the dis­tance from the ceil­ings of the room.

Faults and solutions

First of all, we read about them in the instruc­tion man­u­al in a spe­cial­ly ded­i­cat­ed sec­tion. The descrip­tion indi­cates what may not work and what method will help fix the prob­lem.

The clas­sic rea­sons are unpro­fes­sion­al instal­la­tion and fac­to­ry defects. A detect­ed mar­riage leads to a war­ran­ty peri­od, which aver­ages from 18 to 36 months, but some­times 12 months.

  • Expe­ri­enced engi­neers also point out a false fire alarm in the event of a repair, when dust gets into the device and it goes off.
  • Some­times insects also serve as a cause for unjus­ti­fied anx­i­ety. Rub­bing with alco­hol and blow­ing helps.
  • Loops can peri­od­i­cal­ly noti­fy of a fire with twist­ed wires, where the con­tact is unsta­ble.
  • No one has can­celed elec­tro­mag­net­ic inter­fer­ence from devices, so they must be tak­en into account. Sea­son­al changes, acoustic fluc­tu­a­tions and aggres­sive envi­ron­ments also affect mal­func­tions.
  • False alarms often do not indi­cate the high sen­si­tiv­i­ty of the detec­tors, but low qual­i­ty. Experts also warn that all cheap devel­op­ments lose their lev­el of sen­si­tiv­i­ty over time. And here only a replace­ment will help.

To solve most prob­lems with a mal­func­tion, check­ing the con­nec­tions, the cor­rect loca­tion of the detec­tors and the nor­mal oper­a­tion of the con­tact con­nec­tions will help.

Also, high-qual­i­ty com­po­nents of the detec­tors will help to pre­vent the non-detec­tion of a fire.

Manufacturers and popular models

Fire detec­tors are pro­duced by Euro­pean and for­eign man­u­fac­tur­ers. Among them

  • old­est Japan­ese com­pa­ny Hochi­ki,
  • most pop­u­lar Siemenswhich was joined by the Swiss man­u­fac­tur­er Cer­berus.
  • Fire detec­tors from a British com­pa­ny have proven them­selves well Appo­lo.
  • Also well known Sys­tem Sen­sorwhose prod­ucts are pro­duced in 8 largest coun­tries — from the USA to Europe.

In our coun­try, spe­cial­izes in fire heat detec­tors

  • com­pa­ny “Argus-Spec­trum“locat­ed on the basis of the sci­en­tif­ic and indus­tri­al com­plex in the world.
  • Kit­stroy­servis is one of the lead­ers in domes­tic devel­op­ments.
  • Mag­ne­to-Con­tact pro­duces sen­sors based on sealed con­tacts,
  • a wide range of prod­ucts fromSiber­ian Arse­nal”,
  • research and pro­duc­tion enter­prise “Spetsin­for­mati­ka-SI”.
  • Also, pri­vate enter­prise offers its prod­ucts “Arton” and “Spet­sav­tomati­ka”.


The sim­plest max­i­mum fire-fight­ing ther­mal appli­ances are domes­tic, their price is from 40 rubles to 150.different types of sensors

  • Addi­tion­al options, for exam­ple, a mem­o­ry for a trig­gered device, a light and / or remote indi­ca­tor, an increase in their num­ber entails a dou­bling in price, a spread of 270 rubles. and up to 600.
  • Max­i­mum dif­fer­en­tial sen­sors can be pur­chased for a price of 5 dol­lars. up to 900.
  • One of the best sell­ing mod­els Auro­ra TN (IP 101–78-A1)its price is an aver­age of 7 dol­lars.
  • The most pop­u­lar explo­sion-proof detec­tor mod­el due to its afford­abil­i­ty IP 101–3A-A3R will cost 2 dol­lars on aver­age, although most stores offer explo­sion-proof devices from 800 to 10 dol­lars.

For­eign address­able max­i­mum dif­fer­en­tial devices

  • cost from 10 dol­lars per piece and high­er.
  • Among the address-ana­log max­i­mum-dif­fer­en­tial — best­seller mod­el S2000 IP-03She is stand­ing from 500 to 8 dol­larsbut in gen­er­al, the run-up of address­able detec­tors reach­es 2,000 and even high­er.
  • ther­mal sen­sors — ther­mal cables — depend­ing on the char­ac­ter­is­tics (cable resis­tance, max­i­mum allow­able length, cur­rent volt­age, etc.), they are sold on aver­age from 300 to 7 dol­lars.


Infor­ma­tion about the prin­ci­ples of oper­a­tion, design fea­tures, types and types of ther­mal fire detec­tors will help you choose the most suit­able mod­el in a bal­anced way and with­out unnec­es­sary finan­cial costs. Instal­la­tion rules and reg­u­la­tions are not that com­pli­cat­ed, and if you take them respon­si­bly, you can pre­vent many mal­func­tions. And it is best to car­ry out the instal­la­tion under the strict guid­ance of expe­ri­enced elec­tri­cians.

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