FieldPoint Universal Analog I/O?

[pittpanther]

Hello - I am trying to find an Ethernet-based distributed I/O solution that is capable of handling current and voltage analog inputs on one card. To make this search even more difficult, I need the choice between current and voltage to be dynamic (i.e.: software selectable). I have been satisfied with my previous installations with FieldPoint, and was hoping one of its analog input cards could meet these requirements. My customer is trying to avoid building in the necessary switching circuitry to provide/remove a resistor (via relays, etc.)

Thanks for any input!

Doug

[Aaron_G]

Doug,

Currently there are no FieldPoint modules that offer the ability to switch between voltage and current measurements on the same physical input connection. The FP-AI-100 and FP-AI-110 offer both current and voltage inputs, but the inputs are wired to separate terminals. Using the FP-RLY-422 relay module, you could dynamically re-route the signal between the Vin and Iin pins. Since the input impedance on the current/voltage channels is different, you probably will not need additional resistors.

You will have to be careful with this approach as the imput impedance of the current inputs is 100 Ohms and they are rated for 30 mA of current, which translates into 3 Volts across the current input. If your voltage signals are higher than 3 Volts and you accide
ntly connect them to the current input, you will damage the module.

Regards,
Aaron

[pittpanther]

Aaron...

Thanks for the response. I guess it would be possible to fuse the inputs to the analog card in an attempt to minimize the possibility of damage (of course, we would also develop the soft logic to prohibit this as well). Are the channels optically isolated?

Also, if this style of approach is implemented, and we do dynamically switch the input signal to the analog input card, how would I request the data from the current channel as opposed to the voltage channel via software (and vice versa)? Would I be able to dynamically request the current or voltage signal without having to manually configure it within the FieldPoint Explorer tool?

Thanks again...

[Aaron_G]

Doug,

What software would you be using to control the system? FieldPoint Explorer (and by extension the FieldPoint OPC Server, FieldPoint LabVIEW VI's, LabWindows/CVI driver) does not support dynamic range changing.

However, if you are using FieldPoint serial modules, you can use the !D command (in LabVIEW this can be done using the FieldPoint Optomux drivers), to change the range. Your software will have to know what range you are at to scale the data returned properly. Alternatively, if you are using ethernet network modules, and you are using an NI software product that supports DataSockets, you can dynamically reconfigure the range using a DataSocket connection to the module. The basic technique for using DataSockets is described in t
he following link:
http://zone.ni.com/devzone/conceptd.nsf/2d17d611efb58b22862567a9006ffe76/a6617392b393c4b886256acb0053aebe?OpenDocument

You would want to change the Range item under a channel to dynamically set the range. For a list of valid ranges for your module, refer to the !D command in the FP-1000/1001 Programmers Reference Manual. Regardless of whether channel 0 is set for a Voltage Input Range or Current Input Range, you would address it in software as Channel 0.

As for isolation, most FieldPoint module are channel to bank isolated, not channel to channel isolated.

Regards,
Aaron

[pittpanther]

Aaron...

Our design utilizes Wonderware's InTouch Visualization package for the GUI and their InControl PC based control package. With this software architecture, I am in the process of evaluating Ethernet based distributed I/O solutions that can (hopefully) meet the end user's requirements.

The overall application will involve providing a mobile manufacturing test unit that can walk a user through a series of tests to perform on their completed product (which will involve the testing of a variety of instrumentation that is provided with their end product). This instrumentation can be of many types as well as require a variety of electrical interfaces - therein lies the flexible requirement for a "universal" analog i/o solution
.

It would seem that our given software architecture will not enable the dynamic ranging of the FieldPoint's analog I/O.

Thank you again for your informed responses.

[pittpanther]

Aaron...

Actually, I have evaluated the requirements some more and have realized that even though they do have a requirement to support 0-10V, 4-20mA, RTD, etc. signals - they only "look" at one of them at any given time. Essentially, they will be performing instrumentation testing for a variety of devices - but only one test can be performed at a given time. Ideally, they would like to "connect" all of these devices to our mobile test station (via a patch panel of some sort) - but again, we will only look at one of the devices at a given time. This detail struck me because there really is no need to have multiple physical inputs to our distributed i/o system for a given type. To this end, I am thinking of having a bank
of, say 16, connectors to our tester. Any type of input can be "connected" to any one of these patch panel ports. I am then thinking of some sort of multiplexing of the 16 signals, so that the desired signal can be routed to the proper i/o card. While this solution would require interposing multiplexing, it would significantly reduce the distributed i/o requirements.

What do you think? The only problem I have with this solution is that I can't find a multiplexing device of this nature!

[Aaron_G]

Doug,

There are several ways that you could go about this.
The best method is dependant upon just how much flexibility the system is required to have. You mention 16 signals, with the possibility of current, voltage, or RTD inputs. How much variablity is there on the composition of the signals, is it possible that one test will require 16 RTD inputs and the next 16 voltage inputs, then a third requiring a mix of all type of signals?

The first option would be to create a multiplexer that dynamically re-routes the signals based upon the configuration chosed by the user. I have built test systems in this manner that use several large relay multiplexers to provide flexible system testing that allows me to test or generate the signals for every type of FieldPoint IO module. However, FieldPoint itself does not offer any large density relay multiplexer options although other NI products such as PXI and SCXI do. One type of solution would be a PXI chassis, a PXI controller (why not build the entire computer system in at once), an NI PXI-4070 DMM (offers current, voltage, resistance, diode, and other readings) and an NI PXI-2503 multiplexer (with RTD's you would operate it in the 12x1 (4 wire modue). THis would allow you to route 12 different front panel signals to the DMM, one at a time. Use 2 PXI-2503's and wire them together to get a 24 input system.

A second option, and one that is less complicated, is to simply design and wire the system in such a way that you can provide any type of signal to the measurement system which is capable of reading every type of device. For example, consider a FieldPoint Network module and a FP-TB-10 Dual Channel Terminal base. The FP-TB-10 can mount 6 Dual Channel modules. You could place a FP-AI-V10 for 2 input channels of 0-10 Volts,a FP-AI-C020 for 2 channels fo 0-20 mA inputs, a FP-RTD-PT100 for two channels of RTD inputs, etc... On your front panel, you can wire several input connectors, you can use one set of connectors for current inputs, another set of connectors for voltage inputs, etc... From a software perspective, you can simply display the appropriate channel based upon the user defined configuration.

The two approaches really boil down to how much flexibility the customer requires.

Regards,
Aaron