Application of High-speed Digital Instruments in Testing Firework Products

Application

Testing of Firework Products

Challenge

Testing firework products entails a certain amount of danger, therefore high-standard requirements are imposed on ignition parts of the system. The ignition controller must be highly reliable, capable of ensuring dependable ignition for every single test; while at the same time resistance of relay contacts must be very low, so that it will not affect the ignition performance of the product.

Output performance tests of firework products are transient tests where signal alteration is very quick; it requires high-speed synchronized data capture boards for high-speed data registration.

Firework tests are non-repeatable and therefore require highly dependable data capture boards for ensuring the success of each test.

Firework products involve versatile parameters of output properties. While addressing different product properties, sensors of different types require the arrangement of agile and flexible signal conditioning modules.

Testing of firework products needs synchronized triggering of high-speed cameras, therefore requires capture boards with TRIG IOs for triggering other peripheral devices.

Solution

Based on the design and implementation of a test system with multi-state parameters, via understanding and adjusting signal characteristics of firework product output parameters and commonly used test methods, performance indexes of instruments are analyzed and summarized for the precision testing of output performances of firework products. Combining proper sensors for pressure, temperature, push-force, etc., and hardware facilities such as signal regulators and process controllers equipped with the ADLINK PCI-9846D high-speed data capture card, an ignition controller is designed based on customer requirements, enabling a system not only possessing autonomous detection functions that enhances the safety of the operator when carrying out ignition tests, but also realizing the switching-over between manual and automated triggering. A data retrieval and analysis program for a multi-parameter testing system of firework products is developed using LabVIEW as the development platform. The system incorporates a programmable signal conditioner and functions including data capture, analysis and process, data storage, representation, report compilation; etc.

Firework products is the nomenclature of one-time-use elements or devices, containing gunpowder or explosives which burns or explodes when receiving an external stimulation, used for igniting gunpowder or detonating explosives or doing mechanical work. Firework products are usually used for igniting gunpowder and detonating explosives, or as small drive devices for promptly opening a valve, releasing a safe, or separating a rocket stage.

According to regulations of Nomenclature of Civilian Explosives, GB\T 4659-2003, firework products are generally categorized as follows.[1]

Based on output characteristics, firework products can be categorized into 3 types: igniting fireworks, detonating fireworks, and other fireworks, as detailed in Table-1.

By structure, fireworks can be divided into simple fireworks and complex fireworks.

Fireworks can be triggered by 6 forms of energy, namely mechanical energy, thermal energy, electrical energy, photic energy, chemical energy, and blasting energy. By type of input triggering energy, fireworks can be categorized as detailed in Table-2.

There are many output performance parameters of firework products, such as pressure, push-force, temperature, impact acceleration, displacement, acting time, bridge-wire melting time, delay time, etc. These performance parameters are obtained by providing sufficient voltage and current to the tested product, so as to trigger the activation of the firework product, therefore recording output parameters of the product. In order to carry out various performance tests of versatile firework products using a single set of equipment, and for better and more comprehensive use of the test system, it is necessary to design a comprehensive test system that can be applicable to various firework products. With such a system, multiple parameters of product output performances can be obtained via one simplified test process, providing abundant information for the design of product performances and for the research of functioning mechanisms, as well as providing valuable references for product quality design and for lowering development costs.[2]

Problems encountered

Testing firework products entails certain hazards, therefore high-standard requirements are imposed on the ignition part of the system. The ignition controller must be highly reliable, ensuring dependable ignition of each test; at the same time, the resistance of relay contacts must be very low, so that the ignition performance of the product will not be affected.

Output performance tests of firework products are transient tests where signal alteration is very quick; it requires high-speed synchronized data capture boards for high-speed data registration.

Firework tests are non-repeatable, and therefore require highly dependable data capture boards for ensuring the success of each test.

Firework products involve versatile parameters of output properties. While addressing different product properties, sensors of different types require the arrangement of agile and flexible signal conditioning modules.

Testing of firework products requires synchronized triggering of high-speed cameras and therefore requires capture boards with TRIG IOs for triggering other peripheral devices.

Solution

Based on the demand for configuring a test system, via a market survey of relevant products available in the marketplace, we selected the DEWETRON signal conditioning module and the ADLINK PCI-9846D high-speed data capture card as the infrastructure, and, combined with self-produced ignition controllers, quickly developed an instrument suitable for testing versatile firework products.

The system comprises sensors, a signal conditioner, a process controller and an ignition controller. The system works as follows: When process controller commands, via USB port, the ignition controller to close relay contact, the firework product is therefore in the state of ignition; at this moment, the product bridge-wire will melt instantly to generate a short pulse of voltage signal, i.e., the bridge-wire melting signal and the signal of pressure or push-force acting upon the product. Different sensors are used for testing physical responding signals; weak voltage signal output or electric charge signal output by the sensor is sent to the signal conditioner for amplification up to 5V with high frequencies filtered out. Amplifier gain and filter frequency are set by the process controller via the RS-485 bus. The conditioned signal can thus be read by the capture card. The signal alters quickly, therefore high-speed cards are used for measurement. On completion of tests, data processing and data analysis, data storage and report generation are carried out by the program of the system.

1. Signal conditioner

To meet the requirement that 4 channels of the data capture system shall be capable of connecting with different sensors, i.e., the function of universal channels, the system employs a Dewetron DEWE-31-16 signal conditioner [3].

(1)Major performance indexes of the amplifier:

• Variable input range from ±2.5mV to ±10V
• Programmable Output of 0~12V activating voltage
• Provides internal bridge compensation for 1/2 or 1/4 bridge strain sensor
• Built-in 50K and 100K parallel resistors.
• Supports TEDS sensors.

(2)Filter board major performance indexes:

• 16 channel 2-stage low-pass filter
• Low-noise filter design
• Independent filter frequency for respective channels
• Amplifiers directly controlled by PLC
• Filter frequencies: 100Hz, 1KHz, 10KHz, 30KHz, 100KHz.

2. Capture card ---PCI-9846D high-speed capture card [4]

• 4-channel synchronized sampling, max. sampling rate up to 40MSps per channel.
• A/D resolution: 16 digits
• Channel coupling: DC
• Input impedance: 50 or 1MΩ, can be set via software.
• Clock: local clock, external clock, bus clock, PCI 40MHz
• Trigger method: pre-trigger, post-trigger, intermediate trigger, delayed trigger
• Trigger Level: Trigger Level within measurement range: 256 program controlled setting stages. External Trigger Level: TTL.
• Trigger source: software trigger, digital IO Port trigger, channel trigger
• On-board memory: 512M

3. Ignition Controller

The function of the Ignition Controller is for regulating ignition current, carrying out autonomous inspection of circuit connection, and igniting the product during firework tests.

When constant-current source is used for igniting the product, it is necessary to regulate the ignition current for the product. Firstly, use an ohmmeter to test product resistance. Based on this resistance, adjust the potential meter R7 to the said value and use it as a substitute of product resistance, for current regulation. Then adjust ignition current to the design value, using the voltage knob of power supply and the external potential meter RP2.

When a capacitor is used for igniting the product, firstly move S1 switch to the "Charge" position for charging the capacitor with the battery. By checking the capacitor charge voltage via the static voltage meter, move S1 switch to the "Discharge" position and prepare for ignition.

Before carrying out ignition, make an autonomous inspection; i.e., check the entire ignition circuitry for correct connection. This can be done by ensuring the product is in a condition such that it will not be activated, closing the relay of the autonomous inspection circuit, and checking for any reading of current flowing through the circuit. According to product properties, the current for autonomous inspection must be less than 5mA to ensure that the product is not activated. Therefore, a series resistance required for the autonomous inspection circuit can be calculated based on the maximum ignition voltage of the product.

For the formal ignition test, in order to eliminate any effect caused by the sampling resistor, the system uses a mercury relay in the ignition circuit. The contact resistance of this type of relay is extremely low and can be omitted, thus eliminating any influence to the product's ignition performance resulting from the circuit.

4. Test method

For pressurized products, the test system consists of an on-site portion and a control room portion. Since the testing of enclosed detonators contains a certain amount of danger, the detonator body, plug, pressure sensor and other relevant parts are all placed at the test site, while the ignition control and data capture parts are within the control room, with safety insulation provided between these two portions.

When carrying out the test, after loading test charges in the detonator, transient high-voltage is applied to the ignition resistance filament so its temperature rises and it becomes red, igniting the ignition charge and therefore the test charge. This causes the pressure in the combustion chamber to rise, causing a corresponding alteration of the sensor and an output of a transient voltage, the waveform alteration of which is captured by the high-speed data capture system and registered as the basis of subsequent analysis. Since the test process of the enclosed detonator is very brief, quality pressure sensors and high-speed data capturing systems are essential for ensuring precise and timely capture of the test data. See Fig.6.

In the process for testing firework products, voltage alteration across the resistance is measured before the bridge filament melts down. The test procedure is as follows:

As shown in Fig. 7 when the relay switch is open, the circuit is open and no current flows through the bridge filament, therefore there is no voltage on the sampling resistance. When the relay switch closes, the bridge filament is energized and a high voltage occurs across the sampling resistance; at this moment the firework product ignites and produces high temperatures which cause the bridge filament to melt out, therefore breaking the circuit, and the voltage across the sampling resistance resumes its previous low level. This melting process takes hundreds of microseconds to a few milliseconds. The signal frequency of the voltage alteration is from around a few kHz to tens of kHz.

5. Software Design

The application software is a program developed by the developer using instrument drivers for direct operation by the user. Via direct viewing of the user-friendly interface, abundant functions of data analysis and processing, as well as comprehensive data storage functions, the software completes the test tasks automatically.

Application software of virtual instrumenst can be developed according to personal preferences and specialties using various software development environments. There are two major development environments: one is based on a text software development platform, such as Visual C++, Visual Basic, Delphi or LabWindows/CVI, etc. The other is based on a graphic software development platform such as VEE or LabVIEW.[5,6,7] Our system uses LabVIEW as the development platform of the system program.

The system software can be divided into several function modules: test data input, signal conditioner, system calibration, system auto-inspection, data capture and processing, data storage, report production, data replay and re-processing. The modular design structure enables clear and neat programs as well as facilitating future expansion and upgrade services.