What kind of wire do I need? - Page 1
Forum section: electronics / beginners

author: Jbawgs
author_rank: Newbie
timestamp: June 22, 2023, 12:06:39 am
content: I'm looking for a cable of at least 18awg twisted strand, 7 total conductors, but I need two conductors to be shielded somehow, as 5 are going to carry 120v mains power and two are going to carry an analog sensor signal, and the current 18/7 cable I have causes a ton of noise on the sensor lines.I honestly have no idea if a single cable solution exists, but if it did I wouldn't know what it's called 😅. Additionally, on "real" products I've seen solutions where two or more cables are bundled together but sheathed/shielded individually, but I wouldn't know what that's called either.Any assistance is appreciated.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: June 22, 2023, 01:44:31 am
content: You're not going to get a clean analogue signal out of this. The wire's length alone will be a problem and cause problems with your analogue readings.You should keep parallel runs of "data" cable and "ac" cable 12 inches apart. You're supposed to cross at right angles and try to get a few inches in the gap where they cross. So this is still not good idea.There are plenty of cheap wireless solutions out there now. Look at the ESP32 or ESP8266. They have Arduino libraries. Also, there are plenty of modules out there that would give you some type of wireless comms with Arduino for cheap too. Just make sure the radio you pick is voltage compatible with your Arduino and there's a readily available library/tutorial.

author: Jbawgs
author_rank: Newbie
timestamp: June 22, 2023, 02:08:16 am
content: So what I've built is a esp32 pellet smoker controller, and it works pretty well except for that noise on the two analog sensor lines (it still works fairly well even with the noise).The esp, relays, adc module and 5v supply are all in one box. Two ac mains lines, and three hot ac lines out to the three components of the smoker: auger, igniter, and fan - they share a common neutral outside the controller. The sensor lines are for the pt1000 thermistor inside the smoker. There are other controllers out there that share a similar design and probably solved a similar problem

author: IanB
author_rank: Super Contributor
timestamp: June 22, 2023, 02:21:25 am
content: The thermistor measurement will have a very slow sample rate--a measurement every few seconds, for example? So can't you just filter the signal to remove noise?Also, it seems if the sensor lines are out and back, so any noise should largely be common mode noise, and should mostly cancel itself out. What evidence do you have of an actual problem?

author: Jbawgs
author_rank: Newbie
timestamp: June 22, 2023, 02:26:54 am
content: It samples a few times per second and I'm averaging out in four second blocks (about 30 samples in that time) and it's close. In the raw ads outputs I'm seeing random spikes when the relays come on which alters the output by about 3 degrees fahrenheit.It is MOSTLY getting smoothed out already, but I was wondering if there was such a thing as individually shielded conductors in a 18/7 cable, or something as asked, to further smooth out the spikes

author: IanB
author_rank: Super Contributor
timestamp: June 22, 2023, 02:44:04 am
content: I don't think you are going to find any answer other than the conventional answer, which is that you should keep power and data separate using two different cables. Cable ratings and design are quite different for 120 V AC power cables and low voltage shielded signal cables.The other alternative is to dispense with sending analog voltage signals over a long distance. You could instead use a 4-20 mA current loop which has immunity from interference, or you could encode the thermistor reading and send it digitally.

author: IanB
author_rank: Super Contributor
timestamp: June 22, 2023, 02:49:57 am
content: By the way, if manufacturers are going to produce products in bulk then they could special order cables to meet their needs and pay the cost of having a large production run done to their requirements. You may not find such a thing off-the-shelf.

author: EPAIII
author_rank: Super Contributor
timestamp: June 22, 2023, 02:52:06 am
content: As others have said, line AC power does not mix well with lower level control signals in a single cable. If AC power is really needed at the smoker end of the cable, I would strongly suggest getting it there via a different route. If the two must follow the same path, put the AC in solidly grounded, metal conduit and try to run the control cable an inch or three away (5-10 cm) from even that. But much better would be to separate the two by a number of feet/meters.But if you are only sending the AC to the smoker end in order to power the DC supply, then you could put the transformer, rectifier, and main filter capacitors at the source end of the cable and only send DC through the cable. Do keep additional filter capacitors and the regulator at the smoker end. That would be much better.Another tip is to keep the impedance of the data lines low. Analog signals, like video and audio are transmitted over relatively long distances at Voltage levels around 1 to 3 Volts but using low impedance, shielded transmission lines: 50 Ohms for video and 600 Ohms or lower for audio. Video signals usually use single ended lines while audio often uses balanced lines. There are line driver and receiver chips made specifically for this.As for finding the cable, electronic supply houses stock tens of thousands of different cables. Some of those types do combine shielded and unshielded conductors. Some even have more than one individually shielded pairs inside of an overall shield. You are in the US so: Mouser, DigiKey, Newark, Jameco, etc.https://www.mouser.com/https://www.digikey.com/https://www.newark.com/https://www.jameco.com/

author: armandine2
author_rank: Frequent Contributor
timestamp: June 22, 2023, 07:07:47 am
content: https://www.xylem.com/siteassets/brand/flygt/resources/flygt-resources/flygt-subcab-cables-brochure/might not be wholly applicable - but of course power and sensor wires are used together in pump cables.

author: radiolistener
author_rank: Super Contributor
timestamp: June 22, 2023, 07:11:22 am
content: You can digitize your sensor data on the sensor side and transfer digital data through some twisted line, for example through Ethernet. Power can be delivered through twisted pair (see PoDL - Power over Data Line). If you're needs to minimize count of wires, you can use SPE - Single Pair Ethernet, it allows to transfer data at 10-1000 Mbps rate.If you want higher transfer speed, you can use optic fiber for Ethernet link, it doesn't suffers from mains interference at all.

author: Jbawgs
author_rank: Newbie
timestamp: June 22, 2023, 10:02:39 am
content: Thanks for the tips guys, much appreciated. I'll probably go with a second cable run for the thermistor, measurable interference pretty much disappears at any distance in my tests.

author: tooki
author_rank: Super Contributor
timestamp: June 25, 2023, 04:57:26 pm
content: Quote from: Jbawgs on June 22, 2023, 02:26:54 amIf your controller is controlling the relays, couldn’t you simply modify your code so that temperature measurements are suspended during any kind of switching?

author: wasedadoc
author_rank: Super Contributor
timestamp: June 25, 2023, 05:20:08 pm
content: Quote from: EPAIII on June 22, 2023, 02:52:06 amFYI: Not 50 Ohms. For decades, 75 Ohms (unbalanced) has been the virtually universal standard for baseband analogue video transmission.

author: tooki
author_rank: Super Contributor
timestamp: June 27, 2023, 07:13:01 am
content: Quote from: wasedadoc on June 25, 2023, 05:20:08 pmOut of curiosity, do you knowwhythis is the case, rather than using 50 ohms?

author: wasedadoc
author_rank: Super Contributor
timestamp: June 27, 2023, 11:43:49 am
content: Quote from: tooki on June 27, 2023, 07:13:01 amSee the summary or the full text referenced, both in the post by Wimberleytech athttps://www.eevblog.com/forum/beginners/50-ohm-vs-75-ohm-i-still-don_t-get-it/msg1397915/#msg1397915

author: james_s
author_rank: Super Contributor
timestamp: June 27, 2023, 06:35:40 pm
content: Mixing line voltage and low voltage signalling on the same cable is a bad idea in general and potentially dangerous. What is the line voltage load? If possible I would suggest running 48VDC and using DC-DC converters at the load end to get whatever voltages you need.

author: SmallCog
author_rank: Frequent Contributor
timestamp: June 27, 2023, 11:32:11 pm
content: Look into the methods used for ROV submarines and Geophysical borehole logging equipmentBoth of these combine signals and power over long runs of cableThe geophysical cables likely won't be suitable as they're also weight bearing (basically wire rope with conductors up the centre) but the methods to combat noise may well be worth researching.I imagine the waterproof ROV cable would be prohibitively expensive unless you can get a scrap of it from somewhere

author: radiolistener
author_rank: Super Contributor
timestamp: June 27, 2023, 11:47:12 pm
content: Quote from: tooki on June 27, 2023, 07:13:01 am50 Ω is average impedance between 30 Ω (good for high power transfer) and 77 Ω (good for min attenuation) in coax cable.Usually 75 Ω is used for low power transfer such as receivers because it is more cheap.And 50 Ω is used for high power transfer such as transceivers, but it is more expensive.Here is dependency: