System for durability tests of control modules in the field of consumer electronics. 60 products are tested simultaneously. The products are enclosed in an oven and tempered to various temperatures. Their functionality is measured. This means that inputs of the modules are supplied with simulated signals and the measuring system must monitor the responses of the measured devices at the outputs.
Inputs to the system are:
- 480 dual-valued optotransistors,
- 360 two-valued triac outputs, 220V ~,
- 60 two-value relay power switches.
Outputs from the system, stimulating product inputs, are as follows:
- 120 two-value outputs switching contactors,
- 240 relay contacts 220V ~ 2A,
- 60 analogue outputs simulating a tachogenerator, ie. a sine wave signal up to 42V and up to 2 kHz.
Each of the tested products additionally has a bus (modified RS232) used to set either testing or operation mode.
The system senses signals sampled at same time from all measured products. 32-channel analogue comparator Tektronix 4286 is used, which compares measured values with the set of decision levels. The decision level is set for each measured value in program way. System measures all products simultaneously, so as the measurement speed is considerable. Data going to the program is directly pass / fail logical value on each channel. In addition, the built-in voltmeter makes it possible to measure voltage levels or their maximum and minimum values on any channel. Status change on any of channels causes a program interrupt. At the same time, the module memorizes the value of the input with the exact time of its occurrence (150ms resolution) to the internal memory with a capacity of 1,414 records. This memory can be read programmatically, once at the end of the test.
Measured signals are multiplexed in a pair of Tektronix VX4330 multiplexers. Each one is configured to 16 multiplexers of 30 channels each.
Analog comparators used have an input range of only ± 50V and can withstand 120V between channels. When measuring signals at 220V ~, their range does not match and they would be very vulnerable. Outputs from multiplexers are therefore led to resistive dividers, implemented in the Racal 7064 development module. Galvanic separation of signals to the output level ± 10V is included in dividers. From there, signals go to the comparator inputs. Galvanic isolation enabled use of unipolar comparators.
The 7064 prototype module is equipped with an interface. It is a small board containing a 68000 processor. From this application point of view, it is essential that the processor firmware allows up to 96 bits of TTL-level digital information. In future they can be used to switch divider ranges.
Two multiplexers, supplemented by two relay switch contacts, are used to multiplex two wires of the RS232 serial bus. The bus is therefore multiplexed to one of 60 products. Thus, at a particular point in time, the system can only communicate with one product.
System is equipped with relevant number of relay contacts. It includes a pair of Racal 1260-18 relay boards. Each of them contains 152 individually controlled relay contacts. Of the total of 304 contacts, 240 contacts are used to emulate device contacts. Other contacts are used to control contactors switching high-current conductors (pairs on each measured object) and to switch the serial line.
Module 1260-18 contains relays with contacts that can withstand 220V ~ 2A load. Due to its very high density, it uses a miniature relay with somewhat reduced load resistance, although more than sufficient in the application. Their service life is 108 switches, which is in an average measurement of 1 product per minute almost 200 years.
The Tektronix VX4790A Arbitrary Waveform Generator (ARB) is used to generate tachodynamo simulating signals. The generator generates curves with a maximum sampling rate of 25 MHz with a resolution of 12 bits. A 250,000 sample waveform memory is programmed before the measurement starts and is then automatically executed. It allows change of the amplitude and frequency of the generated signal “on the fly”.
The generator output is fed to 60 isolation amplifiers. All measured products are therefore given the same voltage and galvanically separated from the others.
The computer is connected to the measuring frame by a very fast MXI bus even though there are no special requirements. All VXI modules are housed in one 13-position frame.
A variant to the described solution was in the creation of a measuring device from individual components, using a PC measuring technique. If the costs of development and debugging of individual parts and the whole system are included in the price of this variant, the prices of both variants were comparable. Importantly, however, a system based on standard and open VXI technology gives a number of benefits in use.
The system is equipped with a control program created in TestPoint. This program processes sequences of commands written in a special metalanguage. Commands allow eg.
- read the value of any input in any tested product,
- affect any output of any test product,
- define the communication protocol used by each of the products,
- work with individual bits of digital inputs and outputs of the testing device,
- measure the voltage at the product outputs,
- generate product inputs,
- control the temperature in the test chamber,
- change the supply voltage of the products,
- compare the value findings with the reference values,
- generate error logs,
- coordinate the interoperability of multiple systems,
- describe the wiring of the test cabinet and the individual fixtures,
- define the overall test algorithm.
Use of metalanguage allows modification of the system for future product types using different inputs or outputs, different communication protocol, or having different testing requirements.
User communication with program is in English.
More information request here.