Need help with select a hardware to simulate the high level sensor

[Thang Nguyen]

Hi,

I am working on a simulator project.

I my project I need to simulate a high level sensor. The controller, I work with, has a 5 VDC output, named A. It connects to 4 parallel 10 K Ohm resisters R1, R2, R3, R4. There are 3 switches connect with R2, R3, R4 and this will be correspondent to low, mid, and high level. Another side of these resisters will be connect to ground. Depending on the switch status, the voltage will be drop at the port A. This is how real system works.

I use compactDAQ series C 9172 for my simulator. I tried by using a Analog Output and feeding a voltage output to port A. It doesn't work stable with this solution.

I would like to know if there is any hardware which I can change the resister programmatically? I thought about using a digital output to control a relay to open or close switch. That means I have to buy another 16 DO module which will cost $320 more. I would like to know if there is a better solution for this.

I would highly appreciate your help.

Best regards,

Thang Nguyen

[ShaunR]

You need "current sinking" digital outputs, then you can switch the resistors in direct without relays. The 9172is a chassis. what modules do you have currently?

You could also use the parallel port to switch some relays (be carefull about current though).

Or a non NI rs232 digital board (about $90).

Edited September 9, 2009 by ShaunR

[Thang Nguyen]

I am using NI 9263 Analog Output Module.

I found the module you told me, it's NI 9478. It's a $600 one

[ShaunR]

I am using NI 9263 Analog Output Module.

I found the module you told me, it's NI 9478. It's a $600 one

Not surprised.

Or ya could use one of these or something similar. Google for em.

USB Relay Board

Edited September 9, 2009 by ShaunR

[Thang Nguyen]

Shaun, Could you tell me how to connect the Sinking Digital module with my controller? I have no idea how to use it in my case without using the relay. I add here my real system diagram.

Best regards,

Thang Nguyen

Edited September 9, 2009 by Thang Nguyen

[ShaunR]

Shaun,Could you tell me how to connect the Sinking Digital module with mycontroller? I have no idea how to use it in my case without using therelay. I add here my real system diagram.

Best regards,

Thang Nguyen

OK. So your convinced you need a digital OP. (If you are insistent on NI products compatible with your chassis, I would have chosen the NI 9485 purely because it is 1/2 the price of a digital card but still 4x the price of other alternatives).

From your image I can guess that your sensor port is in fact a constantcurrent source. This makes sense to me as changes in resistance willyield a change in voltage as the load increases/decreases. (This is whyyour analogue output idea won't work).

If you think of a current sinking digital output as a transistor switchto ground. Then (relating that to your diagram) each Digitaloutput would be connected to the other side of the resistor. i.e between the resistor and common. If you are using it in this manner, it is important that you DO NOT connect the External supply to the Digital modules External Power Supply Terminal. This is because internally, each "transistor" is connected to the External supply pin via a resistor. You would in effect be putting this in parallel with all of your other resistors you are using. You also have to remember that it is "inverted logic". i.e setting the output to "1" grounds the device, but this can be changed in the NI configuration if it hurts your head.

Get the NI 9485 unless you are looking for fast IO and it will directly replace your switches and half the price...No brainer!

[Thang Nguyen]

It makes more sense to me when you select this relay module. There is one thing I haven't tell you that I need to measure three tanks like this, so I need 3x3 = 9 channels.

[ShaunR]

It makes more sense to me when you select this relay module. There is one thing I haven't tell you that I need to measure three tanks like this, so I need 3x3 = 9 channels.

NI 9485 x 2