Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

RS-485 milliamp conversion

RS-485 milliamp conversion

RS-485 milliamp conversion

I have a flex IO that is reading 4 weather instruments and reporting the data in milliamps, the data logger that it is sending the data to cannot do the calculation to convert 2 of the milliamp signals to w/m^2 and the other 2 to a temperature in Fahrenheit. does anyone know of a device I could use in between the IO and the data logger to do the calculation and send it to the data logger in W/m^2 and Fahrenheit? thanks in advance

RE: RS-485 milliamp conversion

Well, you need a processor, so something like an Arduino or Raspberry Pi. You could possibly brute-force it with an FPGA designed to do the math, but it's wouldn't be as flexible.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: RS-485 milliamp conversion

Or a PLC with analog-in, then you can have the PLC do any conversion you want.

Keith Cress
kcress - http://www.flaminsystems.com

RE: RS-485 milliamp conversion

I've used the ADAM-6017 for similar applications. It has Analog In and flexible math with a variety of communications options.


RE: RS-485 milliamp conversion

I don’t get the unit conversion at the 4/20mA level.

Presumably the weather device has 4-20mA outputs and is internally scaling each 4-20mA to some range in some engineering units. The temperature signal values are likely scaled in units Deg C, not the desired Deg F.

The datalogger has 4-20mA inputs, receives the 4-20mA signals and saves the data, albeit with limited range scaling conversion ability.

Dataloggers typically export data to a .csv file. The subject line mentions RS-485 - the serial export function? The exported data values, from the datalogger, are reported as Deg C values in the .csv file, not Deg F.

The units conversion from the original Deg C to the desired Deg F is done in the spreadsheet used the view the data, not in the 4-20mA signal.

So I don’t get the need for a converter. Tell me again what the devices are; and which signal they have and where the conversion is needed.

RE: RS-485 milliamp conversion

You make a very good argument Dan. I didn't get the RS485 angle, thinking the OP meant 4-20. We need a bunch more info here.

Keith Cress
kcress - http://www.flaminsystems.com

RE: RS-485 milliamp conversion

I don't get it either. If the signal is already 4-20mA and it is a temperature or irradiance signal then it already has a range of temperatures or irradiances it represents. So, how can you convert a signal that represents a temperature range into a temperature???

The loggers I have used actually did allow me to scale the input to units I wanted so I could read the data directly.

RE: RS-485 milliamp conversion

Ok, I should have been a little more detailed in my OP, apologizes for that. The current set up I Have is a Plane of Array which is a 4-20milliamp device, a Global horizontal irradiance which is also a 4-20milliamp device. A back of module temperature sensor which is a 4-20milliamp device and an ambient temperature which is 4-20 milliamp device. These 4 devices are going into a Flex IO A8332-8f2D, The Flex IO is pushing out the data via RS-485 to the string inverter manufacturer's data logger. The data logger has no calculation capabilities and can only read data coming in, I have been going back and forth with the manufacturer about this. currently, the data logger is just reading values that it is getting from the Flex IO’s registers in milliamps. I need something in between the IO and the data logger that can calculate

((GHI or POA output /1000) *4) *100 = W/m2
((BOM or Ambient output/1000)-4)/16) *130=(-40) = Deg C Temp

So that the data the manufacturer’s logger gets is in the w/m2 and Deg C temp format. Someone mentioned the ADAM 6017 and I am going to look into that one. Thank you guys for your insight

RE: RS-485 milliamp conversion

Thanks for that. What a pain-in-the-butt. Stoopid data logger. It would probably be better to just get a useful one.


To use a logger data one has to actually look at the data in it. To do that you have to use some other program that understands the logged data format. That program is actually where the translation should be. That program also has to know and display the time correctly so the displayed data has temporal relevance. Either find out how to scale the data in that program or simply use a any spread sheet program to create it. Excel or Open Office Calc are excellent examples.

I would seriously oppose doing this electrically. Doing it electrically considerably demotes the system reliability and adds considerably to the maintenance since even more stuff can lose calibration and will need regular calibration.

Keith Cress
kcress - http://www.flaminsystems.com

RE: RS-485 milliamp conversion

Seems like a nitnoid to me. If the units are not what's desired, that can be easily fixed in whatever software is processing the data, so long as the units are clearly spelled out.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: RS-485 milliamp conversion

The datalogger's website mentions a software app, Configuration Console, used to configured datalogger.
But there's no documentation (that I could find), so it isn't clear whether the app allows scaling of the 4-20mA inputs to the datalogger, or not.

If the app doesn't do scaling, then I'm in the group that says that if for some reason, the application that uses this data can't re-scale the data, then replacing the datalogger with one that allows you to scale the data to user engineering units is probably the least costly way to go.

There are devices like Red Lion's Data Station Plus that has configurable COM ports and can be either/and/or a Modbus Master or slave simultaneously and has provision for scripting that can do data scaling, but the learning curve is fairly steep if industrial control systems integration is not your day job.

Tell us again why the app that gets this data can't re-scale the data to your desired engineering units?

RE: RS-485 milliamp conversion

Small brick PLC with an analog input card and RS485 port?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close