Input card with 4 synchronous analog inputs with FleXense technology.
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.
- 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 ArgusOMDS/DynaMaster)
- Proven under harsh conditions (up to IP65)
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.
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.
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.
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.
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.
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.
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.
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.
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.