Which is the best way to monitor 4-20mA sensors in DCE

[GaborNovak]

I would like to monitor 40 temperature sensors, the sensors will measure chiller liquid temperature.

NetBotz systems doesn’t support this amount of 4-20mA sensors. The NBPD0129 is not supported, this product is discontinued.

Which method is the best way to do that?

[APC_Steve]

Hi @GaborNovak ,

If you can still find the NBPD0129, it is supported on the version 3 appliances that support USB such as the 570. Other than that, you've obviously noticed that there aren't enough connections on the 750. You'd really need a lot of them to support what you need. In any case, those connections on the units or the pods are the only way NetBotz can support 4-20 sensors. NetBotz in turn is the only APC supported platform to monitor 4-20 and get them into DCE.

I know of no 3rd party options but that's what you'd have to look for. DCE can only support SNMP and Modbus devices but I know of none that would offer this option.

Thanks,

Steve

[GaborNovak]

@APC_Steve 

The 3^rd party option can be a solution. I know such a device which can read 4-20mA sensors and has RS485 modbus output, the problem that it cannot convert the current readings to physical readings.

I'm searching for some device which can do this task. Reads 4-20mA sensors, convert the measured current reading to temperature and has a RS485 output.

[Shaun]

Hi,

We may be able to handle the conversion on the DCE, depending on the sensor.  The DCE will require a DDF (Device Definition) for a third-party modbus device anyway, eg to instruct the DCE which registers the value lives in.

Most 4-20mA temperature sensors use a linear scale  (eg, for a 0-100C sensor, every 6.25C is 1mA), which is well within the capabilities of the DDF when translating modbus values back to real data.  (I regret I'm too mathematically challenged to promise the same for logarithmic sensors.)

[GaborNovak]

Hi @Shaun

On site there is no measurement the customer wants us to build this system and monitor the readings via DCE system. We can use for example PT100 sensors.

If I’m correct the DCE doesn’t has scaling function. So it cannot convert the current reading to physical value. Is this correct?  I haven’t seen such DDF which was capable to do this conversion.

For example: When we use MODBUS we read the modbus address the return value is our measurement. In the DDF file we can define the sensor type, sensor label, decimal value, sensor increment, etc.

So how to convert in the DDF xml file this current value to temperature value?

[APC_Steve]

Hi @GaborNovak ,

The option @Shaun had mentioned can work. No, DCE has no scaling option available to the user but a DDF specifically designed for this sensor / modbus output combination can handle any scaling, multiplication, etc that would be needed. Each sensor could be converted by the DDF to output data based on the return of the different registers. For instance if 4 mA = 0 degrees and 20 mA = 100 degrees, that should be a relatively simple calculation. 

Steve

[ATrabert]

I agree with Shaun and Steve that the ddf could do this type of scaling as long as it is linear.  However I don't think it's the best solution suited for it. 

Instead you would use a type of IO gateway that reads the 4-20 ma sensor, scales it and converts it into modbus tcp.  Then all the ddf does is read the raw value. 

I would recommend engaging the buildings team, but you should be able to use SmartX AS-P controller and IO modules to do this.  https://ecostruxure-building-help.se.com/bms/topics/show.castle?id=10758&locale=en-US&productversion...

[DavidChild]

Hi,

You can use the EcoStruxures Building Operation's AS-P with the relevant UI modules. Read in the 4-20mA signal into the UI module

Then the temperature reading C of F can be re-transmitted onwards using the AS-P as a slave or server as a BACnet IP/MSTP or modbus TCP/RS485 device.

[GaborNovak]

Hi @APC_Steve 

This kind of DDF will be created by the DDF team? Which information must I provide them to make this kind of special DDF? I would like to test this version to before I make it available for the customer. It is useful to see how it works in real life.

I have an Advantech controller which can read the 4-20mA signal and transfer the current readings over TCPIP modbus communication to the DCE server.

[APC_Steve]

Hi @GaborNovak ,

You'd need to provide them the register map for the sensors you'd want and detail on the sensors, maybe the manual that describes what values in the 4-20 range are equal to what real-life values. Potentially even link this forum post .

Go to https://ddf.ecostruxureit.com/

it just keeps allowing you to scroll but if you search for something (find it or not) the short list will also end with a link for 

Don't see the DDF you are looking for?Submit a request.

I'd copy that link but I'm not sure if it's specific to the browsing instance.

I had already let them know you might be coming.

Steve

[ATrabert]

@GaborNovak you would also need to purchase an asset definition service https://helpcenter.ecostruxureit.com/hc/en-us/articles/360008128678-Asset-Definition-service-for-DDF... in order for the ddf to be created regardless if the monitoring device scales the value or if the value is scaled in the ddf.

[APC_Steve]

That is quite likely but if they have support contracts, they may get to work out a deal before the end of the year.

[GaborNovak]

Requesting new DDF was for free if I remember correctly. Has this option changed?

Our Data Center Expert DDF repository contains the most commonly requested DDFs. New 3rd party DDFs for DCE can only be added through the Asset Definition service. 

Regarding to the article, the free DDF creation is over. I'm right?

I haven’t find the asset definition service in my price list. Could you send an APC Part Number?

We have support contract for the DCE servers and for the nodes. (StruxureWare Data Center Expert Basic Software Support Contract)

I read that in the description that the asset definition service covers 20 DDF creation and 3 modification request to each DDF.

Your DDFs will be delivered on a pre-defined date. Pricing is customized based on the number of DDFs you request. 

So, it’s a bit confusing for me. Where will I become the information about the delivered date and the pricing, etc.  Maybe after the DDF request process via email?

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[APC_Steve]

Hi @GaborNovak ,

I spoke to someone responsible for DDF creation. He stated:

We are doing an interim solution regards DDF credits. The customer must have the following:

• Purchased the support contract before May 20^th 2020
• Provide Serial and MAC of the server and screen shot of their license key page
• Support contract must match the installed license key count

If these are met then we will assign DDF credits free of charge that they can use between now and the end of the current contract.

The skus for the service are as follows

WNSWACS1DDF

WNSWACS5DDF

WNSWACS10DDF

WNSWACS20DDF

The DDF under this service will be delivered within 20 business days and will also include up to 3 revisions.

Thanks,

Steve