Requirements

System for sensing pulse and two-hour data from approx. 900 inputs and measuring 64 analog quantities. The pulse signals represent the rotation of the wattmeter discs, so their frequency is proportional to the instantaneous consumption of the connected appliances. Pulse sensors are designed to guarantee a maximum frequency of 1 pulse per second. The system collects pulse and analog signals, display and evaluates them. During the evaluation it is necessary to take into account the various sampling diagrams and monitor their exceeding.

System components:
  • triple frames VX1410
  • three MXI controllers
  • multimeter VX4237
  • multiplexer VX4330
  • 28 analog comparators VX4286

Pulse and two-valued signals are measured directly, using differential analog comparators with individual threshold and hysteresis settings. Analog channels (low level signals from Pt100 thermometers and pressure gauges with 100Ohm resistive output) are amplified directly in the terminal block and galvanically separated in AnalogDevices 5B Series Single Channel Modules (cubes). The modules modify signals from various types of sensors (strain-gauge, resistance, etc.) or work only as isolation amplifiers. All types of amplifiers (cubes) are plug interchangeable, so they can be freely combined.

28 pieces of VX4286 modules (analog comparator) are used for input of pulse and dual-value signals. Each module contains 32 channels with a range up to 115V and programmable limit (decision) level in the range of 0 to 50V in 25 mV steps (each channel separately – it is possible to individually find the optimal decision level even with disturbed signals) and hysteresis (setting signal falling edge) with the same resolution. Built-in voltmeter measures voltage levels, or its maximum and minimum values ​​on the channels. Changing the status of any of the channels will cause 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 internal memory with a capacity of 1,414 records. This memory can be read from program.

64 analog signals are measured in a multimeter type VX4237. Thanks to the use of the VX4330 relay multiplexer, the number of channels measured is up to 240. The multimeter allows voltage measurements in the range of ±0.2 to ±300V with a resolution of 6½ digits. It is characterized by a long interval between calibrations (one year) without loss of accuracy. FIFO memory for 1000 samples is built-in to store measured data. For some loss of resolution, relatively fast measurements can be performed. Due to the possibility of measuring current, resistance, alternating voltages and currents, the system will also be used for measuring other quantities in the future.

The relay module VX4350 controls signaling devices. The output contacts of each of the separately programmed relay is designed for a load of 220V 2A.

Celková konfigurace systému ..

Modules are located in three VXI frames of VX1410 type. Each frame is equipped with 13 positions; of the total number of 33 positions are occupied by measuring modules and three MXIWIN control modules, so 6 positions remain free as a reserve for further expansion of the system. The control module connects each of the three VXI systems to the computer via a very fast and throughput MXI bus (160Mbps transmission capacity). In addition, each frame is equipped with a company fault monitoring (drop in power supply, overheating, etc.), which reports detected faults, as well as the status of the air filter, via the RS232 serial line to the Master computer.

The industrial master computer is thus connected to a trio of measuring frames by MXI bus used for data communication and by a serial RS232 line used for fault reporting.

All VXI modules are equipped with a self-test that starts when the power is turned on, but it can also be called up from program and program can read results of the self-test. Modules have allow programmable setup voltage level measurement on any channel, which is advantageous for automatic diagnostics support. The computer continually monitors temperatures, condition of cooling air filters and other quantities inside VXI frames.

The VXI-based solution is very compact and is housed in three 19″ (31 cm) frames mounted in a rack. The rack has a depth of 80 cm, a width of 60 cm and a height of about 162 cm. It is equipped with forced ventilation and filters. PC, called Master, controls the measurement, collects data and communicates within the network and to the network to which it is connected.

Experience has shown that the measurement software of a large system is always very complicated. Limitations imposed by original software can only be detected through routine operation. Impact depends very much on how well such software is capable of further development and modification (in terms of copyright, accessibility of source code, productivity of programming tools, clarity and readability, etc.). It is well known that the cost of maintaining programs over their lifetime may exceed their purchase price several times over. Therefore, the optimal solution proved not to buy a finished program, but to develop it to order using a sufficiently powerful development environment. Only the creation of customized measuring and evaluation software ensures that the functions are designed as needed, that is, the software adapts to the requirements and not vice versa. In particular, the user control of the final program can be as close as possible to the conventions of the existing experience, thus facilitating the transition from the existing program to the new one. Above all, however, the further development of the program will be simplified and cheaper.

The measuring program provides:
  • creation of 50 total measuring channels (technological inputs),
  • archiving hourly consumption in technical units to disk,
  • archiving the time of changes of selected two-state values ​​with an accuracy of 0.1 seconds,
  • monitoring compliance with sampling diagrams,
  • display of selected data in technology diagrams on the energy dispatcher display,
  • print daily report,
  • printing of daily balance of hourly consumption,
  • printing of shift energy consumption, daily and running monthly totals, highest mileage maximum per shift, day and month including time of arrival.

Redundancy and dynamic assignment of logical channels to the physical will enable to solve possible failures of one channel by applying its signal to another one.

The solution has the following main advantages:
  • very compact,
  • highly reliable,
  • long time between calibrations,
  • the system will become very slow to morally obsolete,
  • delivery as a whole, guaranteeing the functionality of the system as a whole without the risk of undetected design errors,
  • one partner for solving possible complaints of technology and programs, domestic service,
  • a large margin for future enlargements,
  • possibility to measure voltage, maximum and minimum on all channels, even digital,
  • FIFO buffer for data,
  • modules are VXIplug & play compatible,
  • measuring program developed to order, according to the agreed project, is based on user requirements, so there is no need to adapt its requirements to the finished program,
  • possibility of further modification of the program,
  • direct contact to program authors, hot line,
  • possibility of participation of the user’s staff in the creation of the program,
  • detailed documentation,
  • possibility of lending modules during repair or calibration period.

More information request here.