Project: Help about Relay Modules & Alternatives - Page 1
Forum section: electronics / projects

author: Coolboy4999
author_rank: Newbie
timestamp: July 26, 2022, 01:50:30 pm
content: Hello there.Posting to find some help about the next step on my current project or some alternatives.I'm programming a Keithley DMM7510 (through Python/TSP calls from a PC, using Py-VISA) to measure a item with several measuring points.The objective is to have the PC/DMM automatically take all the measurements necessary without user input (except for the connections of the measuring points to a relay module, which would be done by hand as preparation).One automatic instance of a measuring step would have this sequence (ignoring initial preparation):(PC -> Relay Module) Activate the 2 measuring points necessary for that measurement on the relays(PC -> PSU) Activate, if needed, power supply and load(PC -> DMM) Start measuring script(PC <-> DMM) Read measure buffer, analyse and saveRepeat until there are no more measurementsMy concern regards right now therelay modulepart of the architecture. They should communicate with a PC under some protocol such as ModBus.Taking into account that the largest item currently has almost 40 measuring points, I was projecting having around 45~50 relays ready for the setup (and in case I need more in the future).With that said:Do you believe relay modules are the way to do this? Are there any items sold online you'd recommend?What alternatives are there to relays modules? Or another communication protocol perhaps?Feel free to reply about the rest of the architecture. It may help in other ways too.Thanks for the attention.

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: July 26, 2022, 05:15:54 pm
content: Hello Coolboy4999,on what are you measuring?If it's a pcb than consider building a "Nadelbett" (bed of nails ?)-adaptor that connects to testpointsor use connectors that are used anyways. Manual tp-hookup gets messy, trust me. ;-)For my (SCPI-compatible) switchbox with 192 Relays i use an Arduino with I2C-switch and two busses.Search the net for "Vrekrer_SCPI_parser" or "Lachlan Gunn SCPI" or mail me.

author: macboy
author_rank: Super Contributor
timestamp: July 27, 2022, 01:45:51 pm
content: One thing to keep in mind is the type of relay. You can't use power relays, their contacts are designed to switch higher currents and actually depend on the switching arc to remove oxides. If used with small currents and voltages, they will soon fail to make reliable contact. Instead, you need signal relays or telecom relays. They have contacts plated in gold and/or other precious metals to prevent oxidation. In contrast with power relays, you must never switch higher currents with these or you can destroy this plating.Of course there are commercial products to fill your need. A Keithley 7001 with two 7011-S switch cards having 40 channels each is one solution that comes to mind, because I have it on my bench.

author: inse
author_rank: Super Contributor
timestamp: July 27, 2022, 02:04:32 pm
content: I totally agree on macboys post.You are using a 7 1/2 digit multimeter and if you want to keep the resolution and accurracy, you need to pay attention to the multiplexer/scanner construction.I don't know about your budget, but both scanning multimeters as well as standalone scanners are available.

author: Coolboy4999
author_rank: Newbie
timestamp: July 28, 2022, 02:27:11 pm
content: Quote from: Roehrenonkel on July 26, 2022, 05:15:54 pmThe idea would be to have on every I/O a wire with a clamp and connect it to the measuring points on the item.Furthermore it will operate with at least 15 V and 10 A.I'm not planning on using an Arduino or Raspberry, at least currently. This is being made to work on any PC (Windows), so I guess Rpi/Arduino buses don't apply (right?).Quote from: macboy on July 27, 2022, 01:45:51 pmYes. No power relays needed here. I won't be using more than 10 A. I am aware of those conditions.About your 7001 idea: I just looked it up and it looks very cheap, but it doesn't seem to be TSP programmable, is it? Nor does it have USB/Ethernet inputs, right?I've been looking for prices and alternatives and I've found a reasonable one. I'd like to read your thoughts about it.Idea 1- my initial project, mentioned above:DMM7510, commanded by Python code in PC, working as user interface and measuring device.BUYING relay module(s), commanded also by the Python code in PC through a workable protocol (USB, ModBus,...).I've found a couple apparently good options:Industrial Modbus RTU 8-ch Relay Module, RS485 Bus, Multi Protection (https://www.waveshare.com/modbus-rtu-relay.htm)This is a cheaper option.RS485 Relay Controller - Eight Channel (https://www.kmtronic.com/RS485%20Relay%20Controllers?product_id=73)This one can be bought in larger numbers with a small discount, but still more expensive than the first one.Idea 2- Alternative I foundMeasuring device would be a Keithley 3706A, already bought, with the appropriate switch cards (at least 40 total channels*).DMM7510, commanded by Python code in PC, working as user interface and Master (through TSP-Link) for the 3706A.I haven't messed with TSP-Link (not TSP.Net, right?) yet, but I believe it's a standard Master-Slave protocol, correct?So the idea here would be to send Python-TSP commands to the 7510 that would also command the 3706A.Does that sound alright as an architecture? Practically it sounds like the 7510 is an extra, even hardware-wise, but it's much more flexible and versatile as an interface than the 3706A.* P.S: are there any conditions beyond power and number of channels that I should consider when choosing a switch card?For example, regarding Model 3722 (https://download.tek.com/manual/3700AS-909-01C_Jul_2016_Cards_1.pdf#%5B%7B%22num%22%3A121%2C%22gen%22%3A0%7D%2C%7B%22name%22%3A%22XYZ%22%7D%2C0%2C792%2C0%5D), what does "high density" mean? And what's the drawback, if any, for having so many channels in a single card?P.P.S: For idea2, I just realized I will in fact need a small Relay Module (6 may do) to activate PSU, Load and other power devices when needed. I don't think there's a switch card that can run 10 A, right?