Di­f­fe­ren­ti­al In-Line Charge Am­pli­fi­er

IfTA ChargeAm­pli­fi­er: Ideal for high tem­per­at­ure sensors

Piezo sensors with in­teg­rated amp­li­fi­er elec­tron­ics can­not be used in high-tem­per­at­ure ap­plic­a­tions, as these can­not with­stand the tem­per­at­ures. Here, ex­tern­al charge amp­li­fi­ers are used which con­vert the charge sig­nal out­side the high tem­per­at­ure zone into a voltage or cur­rent sig­nal and can thus also trans­mit it over longer dis­tances.

The IfTA ChargeAm­pli­fi­er is an Ex nA (ATEX Zone 2) cer­ti­fied, dif­fer­en­tial in-line charge amp­li­fi­er that is spe­cially tailored to the re­quire­ments of high-tem­per­at­ure sensors.

High­lights of the IfTA ChargeAm­pli­fi­er

  • Select­able gain from 5 to 250 mV/pC
  • Out­put sig­nal: 10 Vpp
  • In­teg­rated band-pass fil­ter (low-pass at 3 Hz – high-pass 20 kHz)
  • IEPE sup­ply: 8...12mA re­com­men­ded (func­tion­al with 4mA)
  • Com­pat­ible with ICP, CCLD, Iso­tron, Deltatron, Piezo­tron, etc

Data sheet ChargeAm­pli­fi­er

  • Very good 116 dB SNR
  • Ex­cel­lent EMC prop­er­ties
  • Dif­fer­en­tial input (single-ended ver­sion avail­able)
  • Com­pens­a­tion for the pyro­elec­tric "pop­corn ef­fect" with piezo­elec­tric sensors
  • Ex nA (ATEX zone 2) cer­ti­fied (in con­junc­tion with IfTA Ar­gusOMDS/Dyn­aMaster)
  • Proven under harsh con­di­tions (up to IP65)

The Charge Am­pli­fi­er as Part of the Meas­ure­ment Chain

The IfTA ChargeAm­pli­fi­er of­fers Ex nA (ATEX Zone 2) cer­ti­fic­a­tion for ex­plo­sion pro­tec­tion, is sup­plied via IEPE (ICP, Piezo­tron) and is per­fectly suited for piezo sensors in high-tem­per­at­ure en­vir­on­ments.

Ad­vant­ages of the IfTA ChargeAm­pli­fi­er

IEPE sup­ply

The IfTA ChargeAm­pli­fi­er can be in­teg­rated between sensors and meas­ure­ment devices without the need for an ex­tern­al power sup­ply be­cause it re­ceives its power from an IEPE (com­pat­ible with ICP®, Piezo­tron® etc.) This sim­pli­fies the meas­ure­ment chain and makes the charge amp­li­fi­er uni­ver­sally com­pat­ible and in­her­ently short-cir­cuit-proof.

Dif­fer­en­tial input

The IfTA ChargeAm­pli­fi­er is a dif­fer­en­tial charge amp­li­fi­er that en­sures op­tim­al pro­tec­tion against com­mon-mode noise such as mains hum, thus op­tim­iz­ing sig­nal qual­ity. A ver­sion with op­tim­ized CMRR is avail­able for single-ended sensors.

Ex­cel­lent EMC prop­er­ties

In in­dus­tri­al en­vir­on­ments, it is im­port­ant to pay at­ten­tion to the elec­tro­mag­net­ic com­pat­ib­il­ity of meas­ure­ment equip­ment. This as­pect was par­tic­u­larly con­sidered dur­ing the de­vel­op­ment of the IfTA ChargeAm­pli­fi­er and was the sub­ject of nu­mer­ous tests in the EMC labor­at­ory and in the field.

Ex nA Cer­ti­fic­a­tion

A ver­sion with Ex nA (ATEX) cer­ti­fic­a­tion is avail­able for use in haz­ard­ous en­vir­on­ments. With this op­tion, the IfTA ChargeAm­pli­fi­er can be loc­ated in zone 2, and the eval­u­ation/plot­ting unit can be loc­ated out­side of that zone.

Cus­tom­iz­able Gain

In order to ob­tain the op­tim­al gain for all meas­ure­ment chains, sens­it­iv­it­ies from 5 to 250 mV / pC can be se­lec­ted. 5, 10, 25, 50, 100 and 250 mV / pC are avail­able as stand­ard. With the mod­u­lar amp­li­fi­er concept, even in­di­vidu­al cus­tom­iz­a­tions can be real­ized at low cost.

Low Noise

In high-end A/D con­vert­ers, such as those used in the IfTA AD4 line, for ex­ample, 24-bit pre­ci­sion is now avail­able. To make the most of this pre­ci­sion, IfTA ChargeAm­pli­fi­er of­fers par­tic­u­larly low-noise amp­li­fic­a­tion. At 1 kHz, the SNR is 116 dB.

Pop­corn-Ef­fect Com­pens­a­tion

Sensor crack­ers ("pop­corn ef­fect") pose a par­tic­u­lar chal­lenge for the charge amp­li­fic­a­tion of high-tem­per­at­ure sensors. They occur when such a sensor is heated so quickly that thermal stress builds up in the piezo ele­ment. If the ma­ter­i­al sud­denly re­laxes, large amounts of charge are sud­denly re­leased. In simple charge amp­li­fi­ers, the so-called pyro­elec­tric ef­fect can also over­drive the elec­tron­ics for seconds and thus ef­fect­ively blind it.

To meet this chal­lenge, spe­cial meas­ures have been taken to min­im­ize the im­pact of this ef­fect with the IfTA ChargeAm­pli­fi­er. In ad­di­tion, the soft­ware re­cog­nizes typ­ic­al error pat­terns and can take this in­form­a­tion into ac­count dur­ing ana­lys­is, thus avoid­ing in­cor­rect con­trol ac­tions.

The res­ult is a charge amp­li­fic­a­tion with max­im­um avail­ab­il­ity and re­li­ab­il­ity.

Ap­plic­a­tion in Gas Tur­bines

A typ­ic­al ap­plic­a­tion of such a meas­ure­ment chain is the meas­ure­ment of pres­sure in com­bus­tion cham­bers of sta­tion­ary gas tur­bines in order to identi­fy ther­moacous­tic com­bus­tion in­stabil­it­ies. For this pur­pose, the voltage sig­nal that the charge amp­li­fi­er gen­er­ates is sampled by an ana­log input card (e.g. AD4 IEPE). The IfTA Ar­gusOMDS sys­tem per­forms spe­cial ana­lyses of the fre­quency and time do­mains and, via a com­mu­nic­a­tion in­ter­face with the gas tur­bine con­trol­ler, pro­tects the ma­chine against dam­age caused by com­bus­tion os­cil­la­tions. Ef­fect­ive com­pens­a­tion for sensor "shots" is par­tic­u­larly im­port­ant with such ap­plic­a­tions, so that costly un­ne­ces­sary ma­chine shut­downs can be avoided. In com­bin­a­tion with the IfTA Ar­gusOMDS, the charge amp­li­fi­er with piezo­elec­tric high-tem­per­at­ure sensors is used on sta­tion­ary gas tur­bines to pro­tect against ther­moacous­tic vi­bra­tions in com­bus­tion cham­bers.

The Al­tern­at­ive: IfTA AD4Pro with In­teg­rated Charge Am­pli­fi­er

When the dis­tance to the meas­ure­ment sys­tem to be bridged is just a few meters, the input mod­ule IfTA AD4Pro can be used. Each input of the mod­ule has its own in­teg­rated com­plete charge amp­li­fi­er that can op­tion­ally be switched on.

Due to the charge sig­nals short trans­mis­sion paths, this design en­ables op­tim­al sig­nal qual­ity and flex­ib­il­ity. IfTA AD4Pro is also suit­able for mo­bile ap­plic­a­tions, as ad­di­tion­al elec­tron­ics are elim­in­ated. The amp­li­fic­a­tion is con­figured via soft­ware and stored along with all of the meas­ur­ing sys­tem's other con­fig­ur­a­tion data. Espe­cially with lar­ger test setups, this has the de­cis­ive ad­vant­age that changes logged for past con­fig­ur­a­tions can be eas­ily re­stored. Thus, sources of error will be avoided and set-up is more flex­ible.

Re­com­men­ded Products

AD4Pro

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Ar­gusOMDS

Pro­tec­tion sys­tem with dia­gnostics and mon­it­or­ing func­tion­al­ity.

Dyn­aMaster

Dia­gnost­ic tool for high-speed ana­lys­is & in­tel­li­gent visu­al­iz­a­tion.

TrendView­er

Fast & in­tu­it­ive on­line/off­line ana­lys­is soft­ware for ef­fi­cient visu­al­iz­a­tion.