Kayser-Threde has been manufacturing crash test data acquisition systems since 1976. The demands on such systems have steadily risen over the years. The Kayser-Threde engineers have continuously implemented state-of-the-art  technology to fulfil these demands. 1998 Kayser-Threde’s redesign of the on-board measuring equipment lead to a completely new data acquisition system, the MINIDAU® (Miniaturized Data Acquisition System). It was developed in close cooperation with our worldwide customers. Having delivered more than 40000 data acquisition channels to more than 80 customers since, Kayser-Threde is the world leader in this field.

In 2006/2007 Kayser-Threde spent more than one year of engineering in the development of a totally new amplifier for the MINIDAU®. The most modern technology and components were utilized to design and manufacture the latest amplifier inside the MINIDAU®. 

Compatibility was one of the most important requirements for this design. We feel that it is crucial to provide an easy upgrade path to utilize the latest technology, and maintain a reliable product which will be continuously available for many years. The result is the new amplifier for the MINIDAU® Advanced and the MINIDAU® Classic.

The connector panel is designed so that other connector types can be implemented to suit user requirements. Customer demands on connection possibilities for sensors differed enormously and some were even quite controversial. Some of the customers would accept multiple plugs for sensors to achieve a system as small and light as possible, and others just did not want to change from the single plugs they were used to. The combination of a basic system and a full system with a connection panel was the ideal solution for both user groups.

The standard connection panel is fitted with the ODU/LEMO plugs widely used these days in the crash sector. Separating the basic system and the connector panel allows simple implementation of all plug types and pin-outs. Each connection panel on the Minidau® also has a plug to connect an external calibration voltage. This external calibration voltage can be switched to each measuring channel so that the system can be easily checked at any time.

A Minidau® has 32 (96) analog and 16 digital inputs. Each analog channel comprises a programmable input amplifier, bridge excitation circuit, low pass filter and 16 bit A/D converter. The amplifier precision is better than 0.1 % and the input impedance above 10 MOhm. The gain values can be programmed in single steps from 1 to 10 000. An internal reference voltage is used for precise control of the amplifier setting, which is achieved via software loop.

The bridge excitation voltage is programmable separately for each channel. Bridge completion for half bridges can be switched internally. All current sensors may be supplied, a short circuit limitation is provided. In contrast to former designs, the amplifier is designed with adaptive filters which allows the realization of all filter characteristics and  frequencies available. All necessary filtering according to SAE filter classes has to be done in the evaluation and analysis software. 

Each channel of the Minidau® has its own A/D converter with a 16 bit resolution. Thus all channels are sampled simultaneously, ensuring that no time lag occurs between different channels. The maximum sampling rate is 20 kHz. Each channel of the Minidau® has a dedicated D/A converter of its own for compensation of the offset voltage. Neither potentiometers nor trimmers nor mechanical switches are used inside the device. All adjustments are implemented by software, automatically or by command.

The 16 digital inputs come with opto couplers. Each group of 8 inputs has its own galvanic isolated DC-DC converter with an isolation voltage of 100 VAC. By this means simple contacts or switches can be connected to the digital inputs of a Minidau®. Data acquisition systems used in modern crash tests are very reliable. During discussions with our customers, we found out that data is however sometimes lost in exceptional cases. The main error cause mentioned, apart from user errors, was non-registration of the actual crash event (T0 or trigger point).

The measuring system dependency on this trigger point derives from the architecture and design of modern crash systems. These systems are fitted with a semi-conductor memory (mostly SRAM, this means static RAM for increased data security) that normally only allows one recording cycle lasting a few seconds for each channel, because the high sampling rates demand high memory resources in the crash measuring technology.

Up until now, this meant arming the measuring system before the test and then recording the data continuously in cyclic memory. This memory was then filled between the trigger event and the pre-defined post trigger time, and the recording then terminated. An extra backup battery then retained the data for a longer period of time (typically five days).
One of the main focal points in developing the new measuring system was to eliminate the error caused by non-recognition of the trigger event. This problem was solved by considerably extending the recording cycle possible for measured data.

The Minidau® can store data for a 50 s cycle at a sampling rate of 20 kHz which allows the user to start recording data before the vehicle or sled is actually started. This ensures that the measuring system functions correctly and prevents data loss. The trigger point is registered and recorded as in previous systems. Once a valid trigger point is stored in the Minidau® data memory, the user can only select the actual measured data for transfer to a PC, and it is no longer necessary to read out the complete system memory.
 

The Minidau® is designed with a trigger input and output for synchronization with other units. Two analog channels, two digital channels and a remote signal (software trigger) can be selected for triggering. The trigger threshold and trigger criterion can be freely selected for each channel. 64 MB storage are available in the Minidau®.  Batteries are no longer needed to retain the data because Flash-EEPROMs are used for the memory. The data remain available for many years!

The Minidau® system uses an internal battery designed to run the complete system, including all connected sensors, for up to 30 minutes. The K3785 crash-resistant battery is additionaly available for longer cycles. This unit can run a Minidau® System for over one hour. External power supply using trailing cables is of course still possible.

Kayser-Threde offers the a battery based on Lithium-Ion technology, the Advanced Battery Pack . The Minidau® controller itself takes care about charging the battery and guarantees for maintenance-free operation. No tool is necessary to charge the battery. The controller takes care that the batteries are fully charged without any user interaction. The internal circuits finally deliver very precise information (current, voltage, capacity) about the actual state of the battery. The battery pack stores all relevant information concerning production date and charging cycles within module to ensure that unreliable batteries are not used. The battery charging controller is permanently connected to the Minidau® controller via an internal interface and the battery status is then available at any time.

The size of the memory available in the Minidau® demands fast interfaces for data transfer. The standard interface for data transfer is Ethernet with TCP/IP protocol. This interface supports high transfer rates and ensure perfect operation even when long umbilical cables are used. Both commands and data are transferred via this interface.

The Minidau® can be easily integrated in different systems, and compatibility to all CrashLink® systems is of course ensured. In addition to the standard ethernet interface the Minidau® can be fully controlled via RS422.