What is the purpose of Switching & Routing Software?
Within small switching system configurations, or when utilizing just single switch modules, the user typically applies device
drivers with the provided API to control the relays. Simple CLOSE and OPEN commands with additional parameters like module
number and channel number control the required relays.
The user must always take care in order to avoid shorts or malfunctions even when performing simple switching tasks. If there are many relays involved, the risk of error increases significantly.
What problem is trying to be solved?
The example shown below of a 4-wire resistance measurement where a Digital Multimeter (DMM) and the Device Under Test (DUT) is connected to the matrix X-axes turns a simple switching setup into something more complex.
For correct measurement all 4 signal paths between DMM and UUT must be properly set, requiring the cross points on all 4 Y axes to be closed at the correct X position. A single error will produce erroneous measurements or even shorts to adjacent UUT terminals. To extend the 4-wire resistance measurement a second matrix is required and two 2-pole relays can interconnect the matrices on the Y-bus 1 to 4. The control problem becomes more complex as relays are distributed on three different modules instead of one, and each has to be programmed properly to achieve a correct measurement.
It is obvious that switching system complexity increases for signals carried by multiple modules connected to each other are routed through the system.
Switching and routing software aids the management of configuration complexity but has to be easy to use and consider safety issues to prevent inadvertent connections. Switch Path Manager is a solution for this problem.
Switch Path Manager virtually describes any switching architecture and processes all stored project data for switching and routing at runtime. A multivendor and platform independent switch module library provides the models which are added to the project. In addition, the physical interconnections, as well as the endpoints have to be defined. Endpoints are the boundary of the system where measurement and stimuli equipment and all the UUT access points are connected. By calling Point-to-Point or Point-to-Multipoint functions the routing is processed and the required relays are controlled to establish a signal path between these endpoints. The router will never interfere with existing routes and will find an alternate bypass or will terminate with an error message if not successful.
Continuing the first example and extending it to a 4-wire resistance measurement DMM to R2 (Channel 2) there are 4 routes to be established and therefore 4 CONNECT functions to be called. When using the device driver, 18 CLOSE commands have to be sent to achieve the same setup. Besides the increasing number of commands, good knowledge of the system is required to understand which cross points have to be used.
Switch Path Manager with Auto-Routing
- Connect Endpoints (DMM+, R2a) - to disconnect: Disconnect Endpoints (DMM+, R2a), etc.
- Connect Endpoints (s+, R2b)
- Connect Endpoints (DMM-, R2c)
- Connect Endpoints (s-, R2d)
- Close Crosspoints (module1, y1, x1) - to disconnect: Open Crosspoints (module1, y1, x1), etc.
- Close Crosspoints (module1, y2, x2)
- Close Crosspoints (module1, y3, x5)
- Close Crosspoints (module1, y4, x6)
- Close Crosspoints (module1, y1, x29)
- Close Crosspoints (module1, y2, x31)
- Close Crosspoints (module1, y3, x30)
- Close Crosspoints (module1, y4, x28)
- Close Channel(module2, ch3) - to open: Open Channel (module2, ch3) , etc.
- Close Channel(module2, ch4)
- Close Crosspoints (module3, y1, x4)
- Close Crosspoints (module3, y6, x3)
- Close Crosspoints (module3, y7, x1)
- Close Crosspoints (module3, y8, x2)
- Close Crosspoints (module3, y1, x14)
- Close Crosspoints (module3, y6, x6)
- Close Crosspoints (module3, y7, x8)
- Close Crosspoints (module3, y8, x12)
If frequently recurring routes are required it might be more efficient to create fixed routes instead of calling Endpoint-to-Endpoint connections. Those routes can be grouped together to make connecting and disconnecting even simpler. Each separate route holds an attribute called Auto-Route or Static-Route and thus determines in advance whether a route selects an independent path based on the current switch status or a static one, which might fail if an existing route is blocking the way.
For the R2 4-wire measurement 4 single routes (R2_DMM-, R2_DMM+, R2_DMMs+, R2_DMMs-) are grouped (GRP_DMM_R2) and switched by single Connect Route Group commands:
- ConnectRouteGroup (GRP_DMM_R2) - to disconnect: DisconnectRouteGroup(GRP_DMM_R2)
- ConnectRelayGroup (RELAYGRP) - to disconnect: DisconnectRelayGroup(RELAYGRP)
Short Circuit Detection (SCD)
A very important aspect when applying routing software is short circuit detection. If not handled correctly routing might create shorts in a switching system. In below configuration, there are two switching systems interconnected via a normally closed relay. Now, with an existing route established between A and B, a second route from C to D would cause an unwanted short of the two systems. The Switch Path Manager short circuit detection (SCD) prevents this condition, returns an error message and will not switch this second route.
Another, more obvious example illustrates the short circuit detection when using multi-pole relays: Two matrices are interconnected on their Y1 and Y2 lines via a 2-pole relay. The blue and green routes have already been switched. Another signal path from X1 left side and X3 right side would allow a route over one pole of the 2-pole relay, but Switch Path Manager prevents the closing, as on the first pole the green and the blue existing routes would then inadvertently be shorted.
If the switching system's signal leads are not isolated, and therefore used for routing, it can lead to unintended connections
and to short circuits. The two block diagrams below illustrate this within the following task:
establish two independent connections Y1-Y4 and Y2-Y3.
The router searches the best unused path and switches the cross points regardless what is connected. Picture 1 shows an unwanted connection to the DMM+ and s+ leads because at that point the router does not know which signals are applied to given nodes. Picture 2 shows the routes on absolute free paths without any connections to the outside world. This happens because X1, X2, X5 and X6 (used for the DMM) are defined as "isolated" in the system configuration.
For a smooth and easy implementation of switching applications with minimal coding routing & switching software like Switch Path Manager is unbeatable compared to low-level programming. A good and correct setup helps to minimize the risk
of short circuit switching.
The performance speed of routing software should be considered separately. Such systems will always be slower compared to an optimized direct programming, especially when used in small switching configurations with one switch module or a very few. However, these delays are small, in the order of milliseconds.