4-20 ma loop signal generator

V24 current loop recollection comes up

V24?? Wasn't that RS485? Or good old telegraphs interface is definitive current driven, but V24 is a voltage interface as far as i remember.

V24 should be the interface description of signals/"protocol" (if there was any) of RS-232. Looking up in wikipedia, V24 redirects to RS-232, but the article says also " A 20 mA current loop uses the absence of 20 mA current for high, and the presence of current in the loop for low; this signaling method is often used for long-distance and optically isolated links. Connection of a current-loop device to a compliant RS-232 port requires a level translator. Current-loop devices can supply voltages in excess of the withstand voltage limits of a compliant device. The original IBM PC serial port card implemented a 20 mA current-loop interface, which was never emulated by other suppliers of plug-compatible equipment."

The 6850 based V24 port, RS-232 signaling, of my early computing equipment (non-PC) was a 20mA "low noise" type

More recollections coming up - there were line drivers on board. 1488/89 IIRC - those should be the current loop drivers.

4-20mA is the current industrial analogue transmitting standard, 20 mA can represent the high or low analogue value with current levels in between representing some proportion of the signal value, depending on the system requirements. The loop is nominally powdered by a 24V power supply. The output signal is then normally converted by a ADC, this can be a 4, 8, 10, 12 or 16 bit device depending on the accuracy needs of the system. 4-20, is a separate standard to RS232, RS232 and like standards (RS485 etc) are used to transmit the value after it has been converted to digital, value.

so whats left over from early PC 20mA inplemetation is just SolidState control with 20mA current control and good old telegraphy. All lagacy interfaces RS232 are voltage driven upto +-24V which is probanly defined in any ETSI V24 protocol descriptions for Layer1 protocols startbits databits paritybits and stopbits.

RS485 is similar to RS232 but on Layer1 a differential line wiring. Minium 2hot wires and a ground for shielding not as reference. Anyway whi cares all this old stuff its not used in modern computer. Minimum complexity for intercomputer communication is USB in version 1.0 which is overtaken from many newer standards. More and more wireless standards are coming. bluetooth, wlan and UWB interchip communication. Lets see what the far future bringe.

4-20 RS232 & RS485 are very common in process control, Mesh and DCS is gradualy being introduced at the moment within process control of larger plants when large updates are being carried out, but even then for the individual instrumentation loops, 4-20 & 232 or 485 very common with modbus or something similar being used to carry more complex individual item signals, USB & Bluetooth are not commonly used in the outside world. For security, data processing & muxing there are a few other high level communicating standards being used.

Yeah, i have some ruideng e.g. DPS5020 DPS3005 power supplies, they offer bluetooth but the Apps they provide are bad ... they offer also modbus via baseband RS233 3 to 5V or higher IDK to control and readout. I need that one day as simple graph tracer or current over time. Connecting an prolific RS232 to USB and writing some scripts (perl moduls are available im sure) or C code. But no time to make it as a meta solution for future projects to reuse and not do that again and again 😞

At the moment most industrial equipment manufacturers are making gear that will bolt on to existing systems, they are tough, reliable and easy to work with, while PLC, DCS Scada systems can take up the processing slack, some supposedly smart equipment I've come across could be classed as being not very friendly in that they assume that they are the only or most important piece of equipment in the system and if you are using two of them the both want the same id. But overall most basic equipment using the older base line comunication standards do not need to be made more complicated than what they are already, if you have a couple of hundred reporting conditions, let them speak in their low level form of communication and then let the aforementioned higher level equipment sort out the processing, i.e. don't carry out processing on top of processing.

Maybe i have to say again, cuz it was to small. Im looking for tips and tricks and hints for MODBUS. Capture voltage and current, switch outputs on/off nothing more i need.

@hurz, I wish you luck with your project, I worked many years with this stuff, 4-20mA is the main transmitting standard because pure voltage is subject to interference, so all voltages first got converted to 4-20, luckily most equipment used this from word go, then plc's or DCS's converted that to digital. We undestood all the processing and languages involved because of training and the documentation that is around, some of our equipment used modbus and because modbus is proprietary, we had to have a license for each time we had to use it to interface with anything, it was just easier to buy commercial adaptors that already had the modbus license attached as we all ready had to have license's for the systems main DCS's and Scada networks high level language's, so having licenced equipment rather than extra individual process license's was overall easier.

Still not clear, you think i care for any modbus license's if i just use it for private? I give a shit on this license!

Don't need a 1K in f/b loop. Just a link.