Logging 4-20 mA signals and remote access

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Thu, 12/05/2019 - 21:07

Mabille

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.

Fri, 12/06/2019 - 10:55

LabJack Support

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.

Sat, 12/07/2019 - 06:17

Mabille

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.

Mon, 12/09/2019 - 10:37

LabJack Support

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...