SCXI 1102 to acquire current, voltage, and thermocouple from the same module

[Mohammed.Ashraf]

Dear All,

we are now configuring a SCXI system that includes a 32 Channels SCXI 1102 

I know from the specs of this module that it acquires , Thermocouple (of  course with the 1303 terminal block) , Current input signals , Voltage input signals ..

My question is , i have around 14 Thermocouples , 8 Pressure Transmitter (returns 4-to-20mA signal) , and an analog voltage output tachometer (0-5 Volts).. can i use the same SCXI module to acquire all these signals (since they are less than 32 channels) ? or when i configure the SCXI 1102 to acquire a thermocouple input signal , then all the 32 channels will do the same , can i configure this module as a per channel basis ? each channel with it's measurement type(current, voltage, thermocouples) ?

also , when i use the Isothermal terminal block (SCXI 1303) , can i connect directly the pressure transmitters current signal to it an can still read accurate readings ?

I wish you would answer my question as soon as possible , since I have a customer here that wants to place an order and i will discuss the financial offer with him tomorrow

[John_P1]

Hi Mohammed,

You may configure the channels independently.  The timing and triggering is shared across channels, but you can set the voltage range, measurement type, etc. independently.  A basic LabVIEW example might look something like this:

For the current measurements, you will need to provide external shunt resistors across the AI+ and AI- of each channel (I'd suggest using high-precision 249 ohm resistors so the card can take advantage of the full 0-5V range).

Best regards,

John

[Mohammed.Ashraf]

Dear John

Thanks alot for your reply

using a shunt resistor , then i will convert the current to a voltage drop across the high precision 249 Ohms resistor , then why do u name it current measurement ? 

Thanks in advance 

[John_P1]

Hi Mohammed,

That's a good point--we do have the 1308 terminal block for use with the 1102 that has the shunt resistors built-in.  Alternatively, the 1102 has pads available to solder shunt resistors across on specific desired channels (you will probably want to go this route since you have a mix of current and voltage sources).  Appendix E of the 1102 Manual describes the two options.

The marketing for the 1102 describes all of the possible applicaitons for the 1102, but you will need the appropriate terminal block or shunt resistors installed to make current measurements. 

Best Regards,

John 

[Dhika]

Hi,

I am newbie here. I have almost similar question. Can we acquire current, voltage, and thermocouple data using SCXI 1104c together with SCXI 1300?

Thank you very much if you can answer my question. I will be really helpful

[Kyle_A.]

Hello Dhika,

With the 1104C, it is specifically designed for high voltage measurements, and the only range it can be set to do is ±60V, and the gain is fixed.  This means that thermocouple measurements would be inaccurate and unusable, due to the inherent low voltages of thermocouple measurements.  The same goes for current measurements, as the voltage range would severely decrease the accuracy of taking a voltage measurement across a high precision resistor.  The gain on the 1104C is fixed at 0.1, and cannot be switched to amplify low voltage signals.

Some additional information is on page 48 of the SCXI-1104C User Manual, in the FAQ section.  It is suggested that if you wish to make these types of measurements to switch to one of the SCXI-1102 Series modules.

[DYAVi]

I have a smiliar question,

Using the scxi 1102(C) in a real time system, I need to aquire voltages and frequency.  How do I setup the tasks in LabView RT?  Is there a better solution for measureing frequency in a RT application?

[Alisha_P]

Hi DYAVi,

You set up tasks in LabVIEW RT the same way that you set up tasks in regular LabVIEW if you're using DAQmx drivers. LabVIEW RT just adds some added functionality that can be found on the Real-time pallette. Mainly,though, LV RT just allows you to guarantee timing within your VI to a much greater extent.