Sampling Rate for FieldPoint

[India]

I am planning to use the following :

a. FP-TC-120 : 5 Nos.
b. FP-RTD-122 : 1 No.
c. FP-1000 : 1 No.
d. PCI-485/2 : 1 No.
e. RS-485 cabling distance : 500 meters

With this onfiguration could you please let me know how many samples/channel/second can I digitize with clear explanation of the same.

Thanks
Rajini

[Aaron_G]

Rajini,

To start with, I would like to refer you to the following KnowledgeBase Article on FieldPoint Sampling speeds:
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/0d418c9097f14e99862567c300666568?OpenDocument

With FP-1000/1001 network modules it is fairly simple to determine communication rates. With the above configuration, a communication rate of 115200 baud would result in us being able to read all 53 channels (8 channels per FP-RTD-122 module and nine channels per FP-TC-120 module assuming that you want to read the CJ sensor) at approximately 77 ms intervals. A 57600 baud rate would result in communication rates of 109 ms. These numbers were generated using the fp16_rates.vi located at ftp.ni.com/support/fieldpoint/server . How
ever, even though we are reading all of the channels at roughly 10 Hz. The FP-TC-120 has an All Channel Update Rate of 1.13 seconds, which means the actual data is only changing every 1.13 seconds so we will read the same values roughly 11 times before they change. Likewise the All Channel Update Rate on the FP-RTD-122 is 1.08 seconds. Due to the longer distance, 500 m, you may need lower baud rates for good communications. Even if the baud rate was set at 9600, resulting in a scan time of about 430 ms, the FieldPoint modules are sampling at a slower rate so you will be seeing duplicated data.

Regards,
Aaron

[hemmerling]

Hello,

I would like to know the
Sampling Rate for FieldPoint cFP-1804.
http://sine.ni.com/nips/cds/view/p/lang/de/nid/202527
a) with serial RS-232
b) with Ethernet

in number of items ( = channel data ) which can be tranfered.
So of course RS-232 is a bottleneck.

How long takes it to transfer a single temperature data of a

cFP-RTD-122
http://sine.ni.com/nips/cds/view/p/lang/de/nid/11588
, and what is typical maximum number of temperature items transmitted by RT-232 to the PC, per second ?

I read
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/0d418c9097f14e99862567c300666568?OpenDocument

[quote]
The network controllers (FP-160x, (c)FP-2xxx) do not operate in a manner similar to the FP-1000/1001 in that the FP-1000/1001 will respond to poll requests by sending data when they are polled. In order to minimize network use, the network controllers only transmits data when it changes. Basically, the network controllers operates as a data server. The computer will subscribe to input or output items (based upon your IAK file) (Note: with the network controllers it is more efficient to delete unused channels out of the IAK file). When the computer subscribes to an FP-160x's output item, the computer will only send data to the network controllers on change. Likewise, the network controllers will only transmit data from input channels to the computer when on change, so a poll by your program to the network controllers actually goes through Measurement & Automation Explorer (MAX) or FieldPoint Explorer, which gives it the most recent data that it had received and does not physically poll the device. In the case of the FP-1000/1001, it would actually poll the device.
[/quote]

So is cFP-1804 similar to FP-160 ?

In the means that IF the data is changing heavily, the traffic over a serial RS-232 device is maximized ?

What Labview software  is used ? I assume the "Hardware Loop" construction,
where the Labview application waits for new data,

instead of asking for new data 1 / second with a "Timed Loop" in Labview  ?!

If so, I don´t see how to guarantee a certain "sample rate" for applications which need that for data processing ( e.g. FFT ).

I understand that Fieldpoint is for the process automation industry,
but a Fieldpoint solution was offered for a customer lately, who just wants to gain temperature data...

Sincerely
Rolf

[hemmerling]

Also, I don´t understand how I can setup a certain sample speed for

cFP-AI-118
http://sine.ni.com/nips/cds/view/p/lang/de/nid/14874

The data sheet says 10 KSamples/s,
but working together with a dumb backplane

cFP-1804
http://sine.ni.com/nips/cds/view/p/lang/de/nid/202527

I might just may setup the sample rate by the Labview driver,
- is this the right place for that ? -
but I dont´think that I can transfer 10 KS/s by serial device.

***********************************************************************
And who is responsible for the 10KSamples with the CFP-1804,
the driver on the Labview computer or the Analog-Input module ?
***********************************************************************

Additionally

http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/0d418c9097f14e99862567c300666568?O...

This information is primarily valid for the FP-1000 and FP-1001 network modules. The network controllers (FP-160x, (c)FP-2xxx) do not operate in a manner similar to the FP-1000/1001 in that the FP-1000/1001 will respond to poll requests by sending data when they are polled. In order to minimize network use, the network controllers only transmits data when it changes. Basically, the network controllers operates as a data server. The computer will subscribe to input or output items (based upon your IAK file) (Note: with the network controllers it is more efficient to delete unused channels out of the IAK file). When the computer subscribes to an FP-160x's output item, the computer will only send data to the network controllers on change. Likewise, the network controllers will only transmit data from input channels to the computer when on change, so a poll by your program to the network controllers actually goes through Measurement & Automation Explorer (MAX) or Field Point Explorer, which gives it the most recent data that it had received and does not physically poll the device. In the case of the FP-1000/1001, it would actually poll the device.

Is this true for cFP-1804 ?

So if I "want" a certain sample speed, for recording the data by the A/D device, not by the Labview software to get the into PC memory, how to do it ?

Sincerely
Rolf

[Ching_F.]

Hi Rolf,

I would recommend taking a look at the manuals for the products in which you are interested.  The manuals are on the product page (the links you have referenced), under the Resource tab.  The data transfer rates for the cFP-180x are located on page 24 of the manual. 

Since the cFP-180x is a network interface module, not a controller like the cFP-160x, they will not work the same.

Though sampling rate is limited by the module, the data transfer rate may be the bottleneck. 

If you would like to use a different programming language to control your FieldPoint system, you can include support for several different programming languages when installing the FieldPoint driver.  Once you install support, you will have documentation and depending on the language maybe some example programs as well.

Please let me know I you have any other questions.  Best of luck on your application, and have a great day!!

[hemmerling]

Hello,
thanks for the answer.

First I now understand the "artificial" limit of the sample rate of the
cFP-RTD-12x
http://sine.ni.com/nips/cds/view/p/lang/de/nid/11588
devices
of 0.93 Hz, which is true no matter what number of temperature lines are used by the device.

So as we need 10 Hz sample rate, the alternative is to use
cFP-AI-118
http://sine.ni.com/nips/cds/view/p/lang/de/nid/14874
with an extra signal conditioning unit ( by third party, do you know any ? ) to interface the PT100  resistors.

Of course I know the maximum data transfer rate of the serial device of cFP1804
http://sine.ni.com/nips/cds/view/p/lang/de/nid/202527
, it is 115200 bps, from the manual.

But I don´t know the kind of protocol and its overhead, nor if the data is transfered binary or as ASCII strings.
So the question is:

************************************************************************
1) How much data samples ( in # of items ) can I transmit by the serial device, if we use
cFP-AI-118
http://sine.ni.com/nips/cds/view/p/lang/de/nid/14874
which has a maximum transfer rate of 10 KSamples/s, so with 8 channels this is a sample rate of 1250 Hz per channel.
I assume that there the serial device is already a bottleneck

So how many bytes + overhead does a sample take ?
So that I can calculate a transfer rate for samples  like

***************************************************************************************************************
number_of_samples_per_second = (115.200 bps / 8 bit) / number-of-bytes-of-a-sample_plus-overhead
***************************************************************************************************************

We need either 4 or 10 temperature channels ( i.e. 1 or 2 devices cFP-AI-118 ).
Does this fit, at least for 1 device cFP-AI-118 ?

115.200 / 8 bits = 14400 bytes /second.

2) If I use the dumb cFP1804, how do I set the sample rate of
cFP-AI-118
http://sine.ni.com/nips/cds/view/p/lang/de/nid/14874
, by the driver on the Windows PC ? I don´t think that I can set any sample rate in the cFP1804 as it is no controller.

Remember with
cFP-RTD-12x
http://sine.ni.com/nips/cds/view/p/lang/de/nid/11588
it looks if there is no explicit setting of the sample rate, the device JUST produces 0.93 samples / second and nothing but that.

So does the cFP-AI-118 always produces 10KS/s ? I don´t think so...

And even if not, if I just need 4 of 8 channels or 10 of 16 channels, can I configure the system so that 4 or 10 channel data is transfered by the serial RS232 connection ?
I would not ask such "silly" questions for an USB device....

Remember with
cFP-RTD-12x
it looks as if the device scans with 0.93 Hz no matter what number of channels are used...

and somehow the Fieldpoint system looks very primitive... so I ask.

3) If so, and as there is no "intelligence" in the cFP1804, does the cFP-AI-118 send the data automatically by a set sample rate,
or does the WindowsPC and its (Labview) application must ask for a sample each time ?

4)So from the description of the cFP-2xxxx, question is
Does asking the Windows driver for a sample causes the start of a sampling by the cFP-AI-118 ?
Or does asking the Windows driver just causes the "latest" value to be transfered ?
If so this would mean that the process of sampling by the hardware is not strongly "coupled" / "linked" with the process of sampling by Labview
I know that this is ideal for process control, but not usual for instrumentation.
What's true for cFP-1804 ?

5) And is there a full-featured DAQmx driver for the cFP1804 and its modules, with all usual features available with cDAQ and PCI cards, or something else, some unexpected limited  due to the nature of Fieldpoint and/or the serial connection ?

************************************************************************

The real problem is, that for a certain testbed for eletric motors, the manufacturer offers compiled Labview application software wich JUST supports Fieldpoint,
which is quiet unusual  for this applcation.
And so I must find reason WHY not to take Fieldpoint BUT to insist on cDAQ or a PCI card,
and if the manufacturer does not cooperate, why it is necessary to write own Labview software.
So I must proove, why a device dedicated to "process control" with features like "Hot Plugablility" is not the right one for instrumentation of a electric motor testbed.
Especially the manufacturer does not explicitely say if they will offer a TCP/IP solution or serial solution - as we explicitely asked by phone and did not get a positive answer that TCP/IP is offered, we did our own conclusions.

So I must try to UNDERSTAND the limits of the Fieldpoint system.

So any help is appreciated.
Sincerely
Rolf

Message Edited by hemmerling on 01-16-2007 12:17 AM

Message Edited by hemmerling on 01-16-2007 12:19 AM

Message Edited by hemmerling on 01-16-2007 12:28 AM

[RavensFan]

Is it truly necessary to read temperatures at a rate of 10 Hz?  That is a very fast acquisition rate for a temperature measurement.  If you are talking about measurments on a motor test stand, the thermal mass of the motor would be so great that I doubt you would see significant changes in a temperature in a tenth of a second.

[hemmerling]

First of all,
I am electric engineering student and the instrumentation specialist in the ( university ) team, while the rest of the team are mecianical engineering students and so just specialists for the mechanical aspects :-).

The goal is to develop a testbed for SMALL electric motors which are run at 20.000 rounds per minute, with DC currents up to 50 Ampere: Measurment of temperatures at 3 points of the motors,  for up to 24 hours, but with strong increase in temperature at the beginning.

So the devices get hot indeed... and the client, a electric motor company, decides to set the 10 Hz range in the project specifications, as the machines get hot very fast..

So I am not th motor specialist  who later evaluates the test results.

And anybody we talked argued against the 10 Hz :-), while in the same moment everybody agreed "if you want to complete the project successfully, you MUST accomplish this project specification, as it is a mandatory project specification" :-).

Nevertheless, if the company for which we do the project decides to use Fieldpoint as THIS is the one-and-only-offer by the motor testbed company, which refuses to offer a PCI or cDAQ solution, Fieldpoint would be the "platform" for further projects,

because EITHER wie believe the bad talking and bashing against PCI boards in general, by the motor testbed company,
and the bad talking and bashing against the non-available cDAQ solution ( I agree, cDAQ is shit at this moment, as NI advertises a solution where they can´t supply working drivers for, and nobody is willing to put his hands in fire for the next driver releases ),
and AGREE on the Fieldpoint solution,

or we don´t believe the PCI bashing,
and then there is no reason to take the Fieldpoint offer at all.

So for the NEXT project, true analog input is needed, and of course not just with 0.93 Hz.
And then the just-supported serial device is the bottleneck,

and thats why I want to know how many samples / second I may transfer by serial device.
Because if this sample rate is too low,
of course either a Fieldpoint processor must be used for processing the data,
or Ethernet must be used.
Both is not supported by the software of the motor testbench company,

so the question behind is:
Shall we depend on the motor testbench software ( a compiled labview application )
OR
Recommend to write OWN Labview application,

and if so WHY to take Field point ( and not PCI ).

Sincerely
Rolf

[RavensFan]

Hello Rolf,

I would say you really are pinned in a tight place.

On one hand, they are insisting on a 10 Hz temperature measurement.  On the other hand, as you say, they are bashing a PCI method and only providing a fieldpoint method of communicating with the motor test stand.  I don't think there is any way you can get the fieldpoint to get you temperature acquisitions that fast.

Do you have the budget or opportunity to do a hybrid system?  We are finishing development of a test stand.  We chose the compact Fieldpoint for reliability of the control of the stand.  If a bearing temperature goes too high, an oil pressure goes too low, etc., we wanted to make sure the test stand shutdown, so compact Fieldpoint running a real time controller appears to do that for us.  But we also had a need to acquire data from numerous strain gages at a high acquisition rate (5-10 kHz), which the fieldpoint would not be able to do.  So we got a PXI/SCXI system with an SCXI strain gage signal conditioning card that could handle the higher rate.  The PXI computer also acts as our user interface for communicating with the compact Fieldpoint

For your needs, perhaps a PCI with RTD signal conditioning would work for getting the temperatures rapidly, and a fieldpoint system would run the motor test stand.   The question is how much access you have to the fieldpoint software to be able to add on to it to integrate your temperature reading.  Worst case, you have 2 completely separate programs running side by side.  Best case, you have a single integrated program running on a PC and recording data from the PCI while communicating with the motor through the 1804 fieldpoint system.  In our case, we have one program on our PXI for user interface and high speed acquisition and another program on a cFP-2120 for handling the test stand control and acquisition of signals that don't need high speed.  The two programs communicate to each other through shared variables.

[hemmerling]

Its even worse

the 10 Hz is by  the client ( the motor manufacturer
the bashing against PCI is by the motor testbed manufacturer,

we are NOT urged to advise the software of the motor testbed manufacturer,
but we shall advise to take it or leave it 🙂

we are NOT urged to take the Fieldpoint system,
but of course we are frightened when the motor testbed manufacturer tell us about VERY bad temperature measurement experience with older PCI cards (by NI 😞 ) & thermocouples,

and in fact the motor testbed manufacturer was the first who told us *the truth* about the cDAQ system ( no working driver for the PT100 temperature module,  although advertised in official NI quotes from December 2006, first working version is "announced" for Spring 2007,
and NOBODY should expect working drivers for the project period, nobody should depend his job or contract on the promise of working drivers,
so the cDAQ system is no solution for complete 2007 ).

So as we originally intended to advise the cDAQ system, we were taken off the cliffs by the motor testbed manufacturer :-), we can be very glad.

So but if we don´t take the Fieldpoint system, the readymade motor testbed application of this company can not be ordered.

Advising to take any other solution than Fieldpoint
means that the application software must be written from the scratch, by an 6-month internship student ( not us, but maybe somebody of our team takes the job as internship - how about me ? ). Such student is not expected to be Labview expert from the start, and it takes months to get into programming and of course to get into the details of the job ( there are 2 control algorithms to implement in Labview, graphics for the temperature visualisation,.. and if it is nobody of our team, he /she has to become familiar with OUR work)
This means an additional risk, from the point of view of the client.
It is usual that even after 6 month,  many student programming projects are not "usuable" or satisfiying.

Nevertheless we will probably advise the PCI solution  with the condition "high risk",
the Fieldpoint 0.93 Hz solution with "little risk"
the cDAQ solution if the project implementation is scheduled to start in autumn 2008 :-),

but we WOULD LIKE to present a solution with Fieldpoint with  10 Hz,
using the standard analog module cFP-AI-112 or cFP-AI-118,
with an extra extern signal conditioning unit ( which must be bought or self-constructed ) for the P100s.

So what I would like to know no

a) how many data samples can I transfer by the serial device with 115200 bps,
b) now with acitvated or deactivated filters, whats the real sample frequencies of the standard analog modules ?

Sincerely
Rolf

Message Edited by hemmerling on 01-20-2007 12:58 PM

Message Edited by hemmerling on 01-20-2007 01:05 PM