Ten years ago, we announced the Yocto-4-20mA-Tx, which enables signals to be transmitted over a current loop using the 4-20mA industry standard. Designed to be inexpensive, it sometimes showed its limits. Taking advantage of the fact that we had to make a version with a USB Type-C connector, we chose to make some major improvements based on experience with the original product.
Whenever possible, we've taken care to preserve the physical dimensions of the original product for this new version: the Yocto-4-20mA-Tx-V2-C looks just like the Yocto-4-20mA-Tx:
The Yocto-4-20mA-Tx (left) and its successor, the Yocto-4-20mA-Tx-V2-C (right)
Software compatibility is guaranteed: the new version can be used directly with programs designed for the original version. But the USB Type-C connector isn't the only change: in terms of performance, there are some interesting differences...
12V-powered current loops
The first change concerns the loop voltage required to operate the module. Like its predecessor, the Yocto-4-20mA-Tx-V2-C is an isolated module, whose signal transmission electronics are powered directly from the current loop, as 4-20mA sensors typically are. But whereas the Yocto-4-20mA-Tx required a minimum of 12V on its terminal block to operate, the new version only needs around 10.8V. This small difference just compensates for the voltage drop of a 4-20mA receiver at 50Ω on the loop, and therefore allows you to work with a 12V rather than a 24V loop.
Refresh frequency
The second improvement concerns the refresh rate. Whereas the Yocto-4-20mA-Tx can only update the value transmitted on the current loop at around 10Hz, the new Yocto-4-20mA-Tx-V2-C can update its value almost ten times faster. Here's an example of what you get with the two modules if you try to generate a progressive ramp over one second using the CurrentLoopOutput.currentMove() method:
Yocto-4-20mA-Tx only changes value 10x per second. The Yocto-4-20mA-Tx-V2-C does much better...
Latency
In the same vein, the new version considerably improves the delay between loop power-up and the start of signal transmission. Some time ago, at the request of a customer, we released a firmware update for the Yocto-4-20mA-Tx that reduced the latency between power-up and signal transmission to less than 300ms. The new Yocto-4-20mA-Tx-V2-C can do much better:
The Yocto-4-20mA-Tx reacts in just under 300ms. The Yocto-4-20mA-Tx-V2-C in 50ms...
Compromises
Performance improvements have a trade-off: the faster communication electronics consume a little more current on the loop. Whereas the original version could go down to 3mA, the new version is limited to 3.6mA in the standard temperature range, and 3.8mA at 85°C. At the other end of the transmission range, on the other hand, the possibility of transmitting values up to 21mA remains unchanged, so these 21mA can still be used if there's a need to transmit invalid values.
The second compromise we had to make was on price: the more expensive electronic components used in the Yocto-4-20mA-Tx-V2-C raise its price to CHF 46 apiece, whereas the previous version was CHF 37.40 apiece. Of course, you still have the option of buying a Yocto-4-20mA-Tx if the USB micro-B connector doesn't bother you too much...
