Tirin Varghese

Wednesday, February 22, 2023 · 0 min read

ISRO Propulsion Complex

Integrated Signal Conditioner for Aerospace Propulsion Research

What is Dewesoft SIRIUS? For a test engineer, this is a general-purpose data acquisition (DAQ) system only. How strong is your mental and physical health? Is there a way to truly measure it? 

The individual has a very complex nervous system and it is impossible to validate its performance in a single interview. A strong person survives challenges in life, and as consequence, he or she produces the best results for the world. 

Similarly, after multiple evaluations and performance tests (interviews) in various cases over around eight years the Indian aerospace industries have accepted that the SIRIUS DAQ family is the better choice compared to other DAQ systems as it performs a true measurement.

Introduction - SIRIUS R4 data acquisition system

The SIRIUS R4 is a compact high-channel data acquisition system with up to 64 analog inputs, 32 counter inputs, and 32 analog outputs with a built-in high-performance computer and SSD data logger.

Dewesoft R4 DAQ system
Dewesoft R4 DAQ systems each configured with 32 STG analog signal conditioners

Conventional measurement systems are designed and operated according to their functions. They are distributed and interconnected with analog as well as digital buses. It is often more of a choice than a solution. As a result, even though the individual subsystems in the measurement chain offer the best performance the end result is ambiguous.

The unique features of the SIRIUS DAQ systems have eliminated many of these ambiguities that have existed for years for customers. It is a total solution in an integrated manner with more versatile programming features. 

It has a built-in channel-to-channel galvanic isolation, sensor signal conditioner, DualCoreADC® technology with 2x24-bit ADC converter with 160 dB dynamic resolution. It stores precious data in redundant network drives and also presents data in a versatile application-specific graphical and numerical display.

SIRIUS DualCoreADC data acquisition technology with 160 dB dynamic range

The built-in post-processing techniques enable users to analyze measured data swiftly. Furthermore, the reporting features made data sharing and communication easy within the scientific community. SIRIUS DAQ system makes everything under the DewesoftX data acquisition software umbrella and generates a feeling of completeness for the customer. 

So, configurations of SIRIUS DAQ modules (STG, STGm, ACC, LV, HD STGs) with Analog output (AO) - more than 400 analog channels - are running in various subdivisions of the Indian Space Research Organization (ISRO). These signal conditioners are able to connect anything from pressure sensors, charge sensors, strain gauges, load cells, temperature sensors to measure everything needed in modern advanced propulsion systems.

ISRO propulsion complex

ISRO is the main pillar of aerospace research activities in India. It is the key player in the design and development of space launch vehicles. It works on multi-disciplinary technologies like satellites and space technologies for Earth observation, communication, navigation, meteorology, and space science.

ISRO Propulsion Complex

The ISRO Propulsion Complex is one of the main centers doing research and development programs. It is focused on liquid propulsion systems for both satellites and launch vehicles. The mandates of the complex are development, qualification, and acceptance of subsystems, integration of launch vehicles, and spacecraft projects. The Centre has built-in facilities to test/simulate upper-stage rocket engines and thrusters/liquid apogee motors of satellites in a vacuum environment.

ISRO is presently working on the development of a high-thrust semi-cryogenic engine1 based on a mixture of liquid Oxygen and rocket-grade Kerosene, Isrosene. It is a great satisfaction that Dewesoft evolved as a working partner in these research programs. Establishment of the related assembly, integration, and propellant storage facilities are in progress and Dewesoft data acquisition equipment and software are some of the main tools for these missions.

No pain, no gain – the challenges

ISRO research capabilities were limited in the absence of a true measurement system. The measurement ambiguity often reduced their confidence level. The ISRO team was desperately looking for their outdated measurement system to be replaced by a precision measurement system for mission-critical applications. Some of the most recent critical challenges are described here.

Distributed manual system for the quality test procedure

The sensors are deployed in the field hundreds of meters away from the instrumentation station. The signal cables are electrically isolated through an independent instrument. The output of the isolation amplifier is connected to an analog signal conditioner to suppress the bandwidth to the limit. 

The analog output is digitized and transferred through a redundant network and monitored. The analog data is also sampled in the programmable logic controller (PLC) and monitored. Most of these subsystems need manual tuning.

A block diagram of such a conventional measurement system is shown in Figure 1. Scientists have adopted it and are seasoned with their deficiencies. But it was a tiresome and labour-intensive process to set up these types of systems for mission-critical applications and often gave erroneous results.

Figure 1. Block diagram of a conventional measurement system.

Integration of hundreds of sensors and automated measurements

The customer wants to measure more than 200 critical parameters with different types of sensors in an experiment. The sensors were also often changed. It was difficult to manually update the calibration details of the sensor for scaling during the experiment.

Built-in two-point scaling and applying a nonlinear transfer function

The sensors are deployed in the field about a hundred meters away from the instrumentation station. Analog signal losses over the long cable are unavoidable in a distributed DAQ system. The losses in the interfacing cable need to be compensated through a two-point calibration procedure. 

Furthermore, the system has to be programmed to convert the physical quantities by applying a nonlinear transfer function derived from the calibration coefficients. Most of the modern data acquisition systems have only one set of scaling. Hence it was challenging to meet this requirement.

Filters on analog output

Conventional signal conditioners have inbuilt analog low-pass filters at the analog output (AO). So, the AO is wideband low-pass filtered. Even though the SIRIUS instrument is equipped with low-pass filters with sharp cutoff frequency characteristics, it was a challenge for the SIRIUS signal conditioner to make low-pass filters with low cutoff frequency for AO. 

The output delay is a function of the sampling rate in the SIRIUS instrument. Hence it is difficult to achieve the contradicting requirements. A PLC often gives a false trigger with an unfiltered input signal. Hence the customer has to use an additional external filter unit before the PLC.

The solution – SIRIUS signal conditioner

The introduction of SIRIUS DAQ modules at ISRO in 2012 was a game-changer for their programs. It was a totally integrated solution for many issues unanswered for many years. Our hands-on experienced team engineers demonstrated the advanced features of the Sirius modules to ISRO scientists. The team visualized the potential of Sirius compared to existing measurement systems.

We have visited the facilities in ISRO several times and associated ourselves with the scientists to demonstrate a number of tailor-made measurement solutions. We also explored system demonstrations in their experiments.

In short, we have rightly served delicious food when the customer was hungry. Now, our hard work is paying off. Today Dewesoft is a leading working partner for measurement solutions in multimillion mission-critical projects. 

After strenuous efforts over 8 years, we have successfully established our footprint in the Indian aerospace industry. Of course, this gives us new challenges and raises expectations.

Automated integrated system for the quality test procedure

Initially, it was challenging to convince the ISRO team and change their way of approaching the problem. The Dewesoft solution has most of the functions as an inbuilt feature. It eliminated a number of interconnecting cables and potential human errors during the measurement. A few challenges were solved after that.

The Dewesoft solution updated the conventional test procedures with its innovative digital technology. Using our DualCoreADC technology and galvanic isolators in the SIRIUS DAQ system, Dewesoft is always performing one step ahead of any other technology. 

The combination of SIRIUS analog output (AO) with powerful DewesoftX data acquisition software has replaced several pieces of old equipment from their test facilities. SIRIUS analog output is a standalone signal conditioner and its functions are not influenced by software, computer, or any other hardware.

Our solution has several built-in features:

  • isolated programmable sensor excitation,

  • input channel-to-channel galvanic isolation,

  • standalone signal conditioning with analog output digitizer,

  • main and redundant network storage through the DewesoftX NET option,

  • the graphical and numerical representation of raw and scaled data,

  • post-processing and

  • reporting.

DewesoftX Net option demonstration video

Figure 4 is a block diagram of the instrumentation setup for the mission-critical applications with hundreds of sensors deployed in the remote field. Now, the systems are running on integrated single digital technology with modern architecture. Through this setup and method, we have improved the overall performance of the measurement system and minimized manual intervention. The Dewesoft measurement system that replaced the conventional system is shown in Figure 2.

Figure 2: Integrated signal conditioner modern architecture.

Number of sensors and automated integration

The customer has more than 200 inputs with multiple types of sensors to measure various parameters in a single test. It was a cumbersome task to update non-linear calibration details of the sensors manually. 

The only solution we could think of was to import their sensor database into the Dewesoft software. But the sensor database was created in a non-standard text format so we had to convert these data to extensible markup language (XML) for import. 

A small application in Excel enables the conversion of this text file to XML. This file can be imported to Dewesoft analog sensor database. Now, we have successfully interfaced with a nonstandard customer database to Dewesoft. A very useful solution to avoid manual entry errors of different sensor characteristics.

Two-point scaling on raw data and apply nonlinear scaling on the raw data

Figure 3: Non-linear scaling procedure.

A few modern data acquisition systems have only one set of input signal scaling options but they don’t have the option to convert the measured signal to physical quantities using calibration factors. Hence such systems didn’t meet the essential requirement of the customer. The DewesoftX software has built-in novel features to apply two-point scaling on the input analog signal as well as the option to enter a nonlinear transfer function of the sensor from the sensor database (Figure 3).

The customer prefers two-point calibration of the raw voltage as an established procedure. It corrects the signal drops over a long cable. The corrected voltage is further scaled in Dewesoft with calibration coefficients of the sensors to convert the electrical quantities to physical quantities. 

Initially, the raw data is scaled with two-point scaling in an analog channel setup (Figure 4). The nonlinear calibration coefficients will then be loaded from the analog sensor database in the same channel setup. This raw voltage two-point calibration can be enabled in the settings advanced hardware set-up of amplifiers.

Figure 4: Analog channel setup for raw two-point scaling

The raw data and math scaling options are really useful to solve this problem. After implementing RAW offset adjustment in settings, the customer can now do the two-point scaling on raw data. Also, the technicians get scaled value from the math scaling module (Figure 5). Checking raw voltage and scaled value in measure mode itself – it’s now easy.

Figure 5: Math scaling setup (Left) and measured data in raw voltage and scaled values (right).

Hardware filters on SIRIUS analog output

The contradicting requirements of minimum output delay and band limitation at the output signal were challenging. SIRIUS analog output filters work as a function of the input sampling rate and hence the bandwidth. A higher sampling rate gives more quality output with higher bandwidth. 

Even though reducing the sampling frequency will result in the low-pass filtered output it also increases the output delay and is unsatisfactory for a control signal. Hence the customer uses an additional analog filter at the input of PLC.

Figure 6: Proposed digital communication through EtherCAT.

The Dewesoft solution worked on this critical requirement and we are glad to say that SIRIUS analog output was recently upgraded with programmable hardware digital filters starting from 30 Hz. The new analog output is a standalone integrated signal conditioner with hardware programmable digital filters. So, no more need for an additional filter before PLC. This solution is very satisfactory to the customer.

Analog filters SIRIUS DAQ system


SIRIUS, as a standalone signal conditioner, always produces an amplified AO with minimum delay. It is an integrated solution over the conventional distributed measurement system. It stores data using the Dewesoft X NET option to a remote computer in the control room that is situated about a kilometer away from the field. 

The customer analyzes and exports data to different file formats using a custom export rate in our versatile software package. So, the user can interpret and report the test data immediately after the measurement - needing only a minimum of time for preparation.

Compared to a conventional method the overall advantages of this DAQ system configuration:

  • The single-user interfaces with rich visualization for all applications

  • Quick setup for the measurements and fast reporting

  • Total accuracy improvement

  • Sirius-AO is standalone—independent of software and computers.

  • Easy sensor setup update through XML import

  • Programmable excitation for adjusting the field excitation

  • Reduced delay to decision-making controllers

  • Completely synchronized and No settling time for amplifiers

  • Less workforce and more useful space available in the lab

  • The additional mathematics reference curve is available to study the parameter behavior

There are still many jobs to do and applications to be explored in view of this success story. We are confident that a satisfied customer will give us more opportunities. We have further proposed to change the analog output to PLC cable to digital communication via EtherCAT protocol. 

This is a great solution for avoiding copious amounts and lengths of cables and their laying. Also, this will reduce the delay to PLC by replacing the additional filter and analog front-end amplifiers. The details of the scheme are given in figure 6.

Kilometers of cables replaced at a Dewesoft customer with switching from standard analog output signal conditioners to digital EtherCAT interface available on SIRIUS data acquisition systems.

The engineers and managers at ISRO Propulsion Complex trust us. Project success starts in the field where the sensor is mounted and ends with a report of expected results in the customer’s hand. In between, it is brought to life by Dewesoft.


Indian Space Research Organisation (ISRO) official website