4-20ma signal 3

[Ridly]

I have a project that will require a second 4-20ma signal
for recording! The signals as of now goes to a PLC. I would like to get a second signal to run a logging system and use the same currant signal.

 

[itsmoked]

Often the 4-20 is converted to a voltage at the place of use. Can you just parallel that voltage to your recorder?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[danw2]

Most modern devices that source 4-20mA can drive up to 600 ohms of loop resistance.

Each receiver device's analog input has a resistor that converts the current to a proportional voltage.

Two receiver devices can be run in series if the combined loop resistance does not exceed the capacity of the source to drive the loop. Since most inputs do not take more than 250 ohms, it's likely you could run the inputs in series.

If the source is an active output (powered internally) wire it:
source + to input 1 +
Input 1 - to input 2 +
Input 2 - to source -

If the source is loop powered (external power supply) then wire it:
power supply + to source +
source - to input 1 +
Input 1 - to input 2 +
Input 2 - to power supply -

Dan

 

[rmw]

I have often used more than one device in series in a 4-20ma loop but as danw2 states, you have to be careful of the total loop resistance vs capacity of the power supply.

rmw

 

[joecontrol]

There are simple modules that will take one signal and has 2 outputs look up mighty module or API.

I have used these in many places with excellent results.

Joe

 

[powerjunx]

Dan is right: "Most modern devices that source 4-20mA can drive up to 600 ohms of loop resistance" as long as the instrument is within in close proximity that wire resistance never summed up more than 600 ohms, else, instability may occur.


"..the more, the merrier" Genghis Khan

 

[dcasto]

Get an optically isolated splitter. If one leg fails, shorts or whatever, the second leg will be unaffected.

 

[JLSeagull]

Take advantage of the suggestion from dcasto. Search the web for be PDFs from the common signal converter companies such as Phoenix Contact, Moore Industry, P&F, MTL, etc.

 

[IDODESIGN]

Running both your PLC input and Recorder in a series loop is going to be the most cost effective, however should in the future you require to disconnect a device for any reason you will lose all components in the series loop.

A signal transducer as suggested by dcasto is likely your best option, however check the power source. 2-wire signal transducers may require power source on the input or output side of the transducer.

As an alternative you can always take an output from your PLC and connect it to your recording loop. This would minimize your installation costs as you would not have to purchase additional components and nothing extra to install other than wire.

 

[GTstartup]

I agree with IDO that looping all inputs in series is the most cost effective. To prevent the problem he/she describes place a zener across each input (best place is at the terminal strip for that particular input), this way if a device is removed the signal is shunted to the next loop input without loss