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Good grief! Is that the time? Techno Talk Max the Magnificent It’s often not sufficient to simply know that something has happened – the key is knowing when it happened. When there are hundreds or thousands of events, establishing and measuring their level of simultaneity or temporal ordering can be… tricky. I n an earlier Techno Talk column (PE, October 2023) I introduced the concept of Precision Time Protocol (PTP), a.k.a. IEEE 1588, which can be used to synchronise all the nodes in a packet-based network with an accuracy in the sub-microsecond range. Just thinking about how this works boggles my mind. We start off with a ‘grandmaster clock,’ which will probably derive its notion of time from some global navigation satellite system (GNSS) source. All the downstream nodes in the network will maintain their own local time-of-day (ToD) clocks, often with battery backup, but how do we (and they) know how accurate they are? This is where PTP enters the picture. The network node associated with the grandmaster clock will send a data packet to one of its downstream nodes. This packet will be timestamped as it leaves the grandmaster and timestamped again on arrival at its destination. The downstream node will then return the packet to the upstream node (the grandmaster in this example). Once again, the packet will be timestamped both on departure and arrival. By means of these four timestamps, the upstream node can (a) calculate the round-trip-time of the packet and (b) determine any error in the downstream node’s clock. The upstream node can subsequently transmit a control packet to the downstream node saying something like ‘You are xxx out of sync, so set your local time-of-day clock to yyy.’ Of course, things are a lot more complicated than I’ve made them sound here. For example, different packets can take different routes through the network. Also, each upstream node may have multiple subservient downstream nodes, and each downstream node may be seen as an upstream node to other nodes that are further downstream, if you see what I mean. Feelin’ the strain? The reason I’ve been waffling on about PTP is that I just discovered its use is not limited to things like 5G radio access 8 networks (RANs). I was talking to the chaps and chapesses at VTI Instruments. These little scamps design and deliver data acquisition and functional test solutions for anyone designing large structures like wind turbines, airplanes and small modular reactors (SMRs), which are small nuclear power stations with power generation capabilities in the 30MW to 300MW range. Strain gauges were invented by Edward Simmons and Arthur Ruge in 1938. The most common type of strain gauge consists of an insulating flexible backing that supports a metallic foil pattern. The gauge is attached to an object of interest by a suitable adhesive. As the object is deformed, the foil is deformed, thereby causing its electrical resistance to change. By measuring this change, it’s possible to determine what’s happening to the structure to which the gauge is attached. The folks at VTI make a 16-channel precision bridge and strain gauge unit. To minimise errors, these units need to be placed close to the strain gauges they are monitoring. ‘Not a big problem,’ you may think. OK, but now suppose I tell you that the folks testing a large prototype aircraft may have up to 10,000 strain gauges in play at any one time. This means they need 625 of these 16-channel strain gauge units. LAN eXtensions for Instrumentation (LXI) is a standard developed by the LXI Consortium, which maintains the LXI specification and promotes the LXI Standard. This standard defines the communication protocols for instrumentation and data acquisition systems using Ethernet. VTI’s strain gauge units employ the LXI standard to transport the data they are reading over Ethernet cables. Obviously, we don’t have 625 of these cables feeding directly into a server. Instead, groups of (say) 16 cables will be fed into a bunch of 16-port Ethernet switches. There will be a hierarchy of these switches leading to the main server. Also, as opposed to deploying 625 power cables, the 16-channel strain gauge units employ Power over Ethernet (PoE). But the really important point about all this is timing. Suppose the team is performing a structural test to determine when a wing will break, for example. In this case, it’s not sufficient to simply know the readings on all the strain gauges over time – it’s critical to know the exact times associated with each of the readings. You can only imagine my surprise to discover that VTI’s strain gauge units include support for PTP/1588, thereby allowing the times of, and relationships between, events to be determined with sub-microsecond accuracy. Can’t take the pressure? Suppose we are building a small nuclear reactor like one of the aforementioned SMRs. One thing we can expect to find at the heart of the SMR will be a lot of pipes. For example, there will be a coolant circulation system that powers the turbine that drives the generator that produces the electricity. Some SMRs use water as a coolant. Heated by the reactor core, the water turns into superheated steam that powers the turbine. Other SMRs may use gas, liquid metal, or molten salt as coolants. Not surprisingly, we are going to be interested in the pressures at various points in our piping networks. Also not surprisingly, we are going to be reluctant to use standard pressure gauges, which will oblige us to drill holes in our pipes. Every hole and every weld are potential points of failure. The solution, once again, is to employ strain gauges. Measurements from strain gauges can be used to determine stress, deflection, torque and deformation. In the case of pipes, deformation can be used to ascertain the pressure of the fluid (liquid or gas) in those pipes. My eyes have been opened I was introduced to strain gauges when I was a student in the dim and distant past. I must admit I didn’t hold them in particularly high regard at that time, but I think it’s fair to say that my eyes have been opened to a world of possibilities. Practical Electronics | December | 2023