In high-temperature applications for piezoelectric pressure sensors, the electronics for charge amplification cannot be integrated into the sensors. This applies to measurements taken, for example, in the combustion chambers of reciprocating engines or in gas turbines. In these cases, external charge amplifiers are used, which convert the charge signal to a voltage signal outside the high-temperature zone.
With the Ifta ChargeAmp, IfTA has introduced a new Ex nA (ATEX zone 2) certified differential in-line charge amplifier to the market; one specifically tailored to the requirements of high-temperature applications.
- 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.
- 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 OMDS / DynaMaster)
- Proven under harsh conditions (up to IP65)
The IfTA ChargeAmp can be integrated between sensors and measuring 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.
Ex nA certification
A version with Ex nA (ATEX) certification is available for use in hazardous environments. With this option, the charge amp can be located in zone 2, and the evaluation/plotting unit can be located outside of that zone.
The IfTA Charge Amp 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.
In order to obtain the optimal gain for all measuring chains, sensitivities from 5 to 250 mV / pC can be selected. 5, 10, 25, 50, 100 and 250 mV / pC are standardly available. With the modular amplifier concept, even individual customizations can be realized at low cost.
Excellent EMC properties
In industrial environments, it is important to pay attention to the electromagnetic compatibility of measuring equipment. This aspect has been given special consideration in the development of IfTA Charge Amp, the development phase of which was the subject of numerous tests, both in the EMC laboratory and in the field.
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 charge amplifier offers particularly low-noise amplification. At 1 kHz, the SNR is 116 dB.
Sensor cracker during the charge amplification of high-temperature sensors presents a particular challenge. They arise when a sensor is heated so quickly that thermal stresses build up in the piezoelectric element. If a sudden expansion of the material occurs, large amounts of electric charge can be abruptly released. In simple charge amplifiers, this so-called pyroelectric effect("popcorn- effect") can overload the electronics for seconds and effectively blind a sensor.
To meet this challenge, special measures have been taken to minimize the impact of this effect with the IfTA Charge Amp. In addition, the software detects the typical pattern of a sensor "shot" and can take this information into consideration during the analysis.
The result is a charge amplifier with highest availability.
Application in gas turbines
A typical application for such a measurement chain is the measurement of pressure in the 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 OMDS 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 spurious shutdown of the machine can be avoided.
The alternative: IfTA AD4Pro with integrated charge amplifier
In situations where the distance to the measuring system to be bridged is just a few meters, IfTA AD4Pro can be used. Each input of the measuring board has its own integrated full-fledged optionally-switchable IfTA ChargeAmp.
Due to the charge signal's short transmission paths, this design enables optimal signal quality and flexibility.
This option 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.