11.2. Spark safety remote I / o

In the previous section we discussed the construction of intrinsically safe I / O with the use of barriers. However, often such a linear approach is not justified. Situation will be clarified following illustrative example: let's designed control system with the number of signal input / output (1000 EX IOs), which must be intrinsic safety, reaches thousands. Consider what equipment it would require. First, we must organize itself I / O to 1000 channels. Secondly, it is necessary to ensure the intrinsic safety field signals by means of suitable barriers. At an average price of a barrier in the 160 Euro (This is the average price barriers for analog and digital signals) of their total value will be 160 Euro x 1000 = 160 000 euros. Moreover, this price does not include additional sources of supply, cables, terminal devices and related mounting part. In view of all listed, the cost of solutions for spark protection could rise to 180 000 - 190 000 euros. This very impressive amount is cause for reflection.

Fortunately, there are more elegant, and most importantly - cheaper, solution. Many manufacturers APCS combined subsystem remote input / output and standard of intrinsic safety barriers in a single modular device, and gave him a complex called "node intrinsically safe remote I / O" (Intrinsically Safe Remote IO, or abbreviated - IS RIO). The peculiarity of this device is that INDICATORS connected circuits implemented in field I / O modules, and the device is designed for installation directly in hazardous areas (Ex-zones).

As an example, in Fig. 1 - 50 shows the node IS RIO ET200iSP series produced by Siemens. Nodes ET200iSP allow installation in Ex-Zones 1, 2 and serve to connect sensors and actuating devices operating in Ex-zones 0, 1 and 2.

Fig. 1 - 50. Node IS RIO of series ET200iSP by Siemens

As seen from the figure, the design and appearance of the node IS RIO is not much different from the usual site remote input / output (discussed in "Field I / O ..."). By analogy, one can distinguish the following hardware modules:

1. Explosion-proof power supply (or redundant power supplies).

2. Intrinsically safe interface module (or redundant pair of interface modules).

3. Intrinsically safe I / O modules.

4. Terminal panel.

Each I / O module is installed on your terminal bar, which are connected via screw terminals signal wires of the field input / output. To install the interface module is slightly different terminal panel, which together are connector terminals for connection to a digital field bus (Figure DB9 connector for bus Profibus DP). There is also a special terminal panel to install the power supply. All terminal panels are mounted on a standard profile rail or DIN-rail in the following order: first set terminal panel power supply (or two redundant power supplies), followed by the terminal panel interface module (or a pair of front-end modules), followed by terminal input panel module and output. When interfacing terminal panels formed an integral internal bus, which passes through the entire assembly. On this bus to exchange information between modules installed and electrical connections for them. I / O modules type similar to that used in conventional systems, I / O: AI, DI, AO and DO. Number of channels of analog modules ranging from 2 to 8, discrete - from 8 to 16.

Nodes IS RIO, as a rule, support the installation of up to 8 I / O modules. This is severe restrictions on the total power consumption. When you build a site it is very important to make sure that its total consumption does not exceed a certain limit (specified in the enclosed design guide), otherwise it could lead to an excessive load on the power supply, and reduce the current unacceptably high level of explosion. In all modern systems of IS RIO may be "hot swappable interface modules and I / O modules.

Interface module allows you to connect a node IS RIO to the digital bus data using a standard communication protocol. This module typically performs the functions of the slave device. The most common protocols Profibus, Modbus, and ControlNet.

Fig. 1 - 51 presented to the node IS RPI (Intrinsically Safe Remote Process Interface) company Pepperl Fuchs. Note that unlike ET200iSP, this device is not backed up. Also striking that the power supply is not installed on the terminal panel in conjugation with other modules of the site and installed separately (in the figure the power supply does not shown). A characteristic feature of this system is an extended operating temperature range from -20 ° C to +70 ° C, which allows installation IS RPI in closets without heating in unheated rooms and the street (in the average climate conditions).

Fig. 1 - 51. Node IS RPI of company Pepperl Fuchs

Consider all the advantages and disadvantages of using IS RIO for example. Fig. 1 - 52 presented the classic approach of the input / output. Each channel I / O connected via IS-barrier. Actually, nothing new in this scheme, no - it was all discussed in detail in the previous section.

Fig. 1 - 52. The scheme of using intrinsic safety barriers

Now the scheme slightly optimize and introduce IS RIO. The result is shown in Fig. 1 - 52. The controller in the digital bus connected nodes IS RIO, which are in the explosive zone 1 near the field equipment. The very same field equipment generally located in zone 0.

Fig. 1 - 52. Scheme of intrinsically safe I / O on the basis of IS RIO

Pay attention to the digital bus (IO BUS), connecting the controller and the nodes IS RIO. Some of the tire is in hazardous areas, so for her, as for the field signals to provide a reliable spark protection. This is done by dividing the barriers to digital bus (Bus Couplers), installed in the safe zone. For example, such a barrier can send pictures Profibus DP protocol for the special bus, built on the basis of physical-level IS RS-485 and which is intrinsically a modification of conventional RS-485. Some systems IS RIO supports connection to an optical digital networks and, naturally, does not require any barriers bus (fiber in principle can not be spark dangerous). Such systems are available, for example, the German company Stahl.

Nodes IS RIO are not fastened to the wall in an unprotected form, and are installed in a special box (boxes) for hazardous areas. Shells intended for zone 1, are produced in accordance with explosion protection type EEx e (increased safety) and have a degree of protection not less than IP65. These shells are robust rubber seals, and cable connections are made with screw connections and securely sealed. For Zone 2 safety requirements more democratic. Fig. 1 - 53 shown mounted closet system IS RIO:

Fig. 1 - 53. Example of mounted shelf of system IS RIO

The advantages of using the system IS RIO are obvious:

1. Reducing of cable routes. In contrast to the barriers, IS RIO units can be installed close to the sensors and actuators, and digital signal input / output are transmitted to the upper level of a two-wire digital bus.

2. Minimization of equipment. Each module I / O system IS RIO, in fact, serves two functions: a direct input / output field signals and providing INDICATORS connected to the field circuits.

However, it would be unfair not to mention one serious drawback: need a sufficiently large amount of work to configure the network interface between controllers and hosts a top-level IS RIO, which are often in relation to the controller, a third-party devices. In general, the practice shows that the use of IS RIO justified at high density of intrinsically safe signal input / output, when they accounted for less than 30% of the total number of signals, in which case the cost of organization-level I / O may be reduced by 20 -- 25% compared with the decision based on the classical barriers.

12. Alarm and archiving which are in distributed control systems

Archiving process parameters - the inherent requirement for all modern systems of governance. In fact, advanced system backup - this is a characteristic that distinguishes CSF from numerous full-featured, so to speak, "analogues".

Why do need archiving process parameters? For three very simple reasons:

1. Archive of values of technological parameters (in technical jargon - the history, history) to evaluate the quality and effectiveness of the control system. This is done through a retrospective analysis of key process parameters, which gives an idea about the extent to which achieved the goal of management.

2. Archiving allows experts to assess the dynamics of technological change over a long period of time, which is extremely useful for understanding the behavior of the process in different (including emergency) situations, and, consequently, the acquisition of knowledge about a particular technology.

3. Archive can contain information that helps to establish the causes of various accidents and emergencies. Thus, having carefully studied the log of actions of the operator, a technician can determine what kind of transaction manager has led to a deviation from the regulations or by accident (we can assume that the awareness operators that their every action is logged the system, largely of their disciplines).

What information is archived (written in history)? In general, all data that is stored in the archive can be divided into three groups:

1. Process variables (process values).

2. Alarm (alarms).

3. Actions of operators, technologists (operator actions).