Logging 4-20 mA signals and remote access | LabJack
 

Logging 4-20 mA signals and remote access

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Mabille
simon.nordestgaard's picture
Logging 4-20 mA signals and remote access

Hi,

I have several 4-20 mA signals from different sensors for a trial in a large factory. 

I would like to log the values and be able to access the data remotely. 

I was thinking about getting a LabJack T4, with several JTick-CurrentShunts, as well as a NetGear LB2120 modem (http://www.netgearinnovation.com/au/best-4g-modem/).   

Should this be possible using the equipment mentioned and with the software that comes with it? Are there other better alternatives that I should consider?

Thanks for your help.

LabJack Support
LabJack Support's picture
Hardware sounds good and that

Hardware sounds good and that modem should get you connected to the Internet.  The trick is how to you talk to a device on some other network through the Internet.

https://labjack.com/support/app-notes/networking/labjack-internet

https://labjack.com/support/app-notes/networking/labjack-internet/appendix-A

Check out the last 2 options on that last link:  remote desktop or port forwarding.

 

Mabille
simon.nordestgaard's picture
Many thanks.

Many thanks.

I also will be using a piece of equipment in the trial that has a Siemens PLC and HMI (TP100 - https://mall.industry.siemens.com/mall/en/WW/Catalog/Product/6AV2124-0JC...) that will have various parameters (flow rates, temperatures, pressures, etc.) on it that I will also want to log and be able to access remotely. Should it be possible to connect this to a T4 and that modem as well and access the data remotely? 

Sorry, one further question. If data logging with the T4, is it possible to assign a time to each data point in some way? In the comparison of devices it says that only the T7Pro has a real-time clock.

The T7Pro doesn't have the 0-2.5V range like the T4, only +/- 10V, so would the resolution with the LJTCS be poorer?

Thanks again.

LabJack Support
LabJack Support's picture
Should it be possible to

Should it be possible to connect this to a T4

If the PLC has analog outputs, you can have it output voltages related to your desired signals and then the LabJack can measure those voltages.

As for digital communication, the PLC/HMI is likely a Modbus TCP client, and the T4/T7 is a Modbus TCP server, so the PLC can read registers from the LabJack but not the other way around.

Perhaps the PLC/HMI can behave as a Modbus TCP server, like the LabJack.  Then if your software is a Modbus TCP client (e.g. any SCADA software) it can read from the PLC and the LabJack.

 

If data logging with the T4, is it possible to assign a time to each data point in some way? In the comparison of devices it says that only the T7Pro has a real-time clock.

The real-time clock on the T7-Pro is generally only applicable to standalone datalogging:

http://labjack.com/support/datasheets/t-series/sd-card#standalone

http://labjack.com/support/datasheets/t-series/lua-scripting#involveahost

Your system sounds like it not try to use the T7-Pro as a standalone logger, but rather will have a host with software involved.  The software can assign timestamps to samples using the system clock of the host.

 

The T7Pro doesn't have the 0-2.5V range like the T4, only +/- 10V, so would the resolution with the LJTCS be poorer?

The T4 is a 12-bit device so resolution on the 0-2.5V range is 2.5/4096 = 610 uV at best and that does not include any noise.

Yes, the T7-Pro does not have a perfect input range for a 0-2.5 volt signal, but because it has 16-bit and 24-bit converters it does better anyway.  To measure a 0-2.5 volt signal with the T7-Pro you would use Range=+/-10, so see the first part of Table A.3.1.1 and you can see that the effective resolution is 316 uV down to 5.7 uV:

https://labjack.com/support/datasheets/t-series/appendix-a-3-2-2-t7-nois...