connect two digital indicators whose input is 0-2 volts and output is RS 232 serial interface to com1 and com2 ports of computer

[shrutimv]

i'm constructing a differential thermal analyser.I have the readings in volts from the reference junction connected to a 

Digital Indicator, Mains 230V AC Operation,

Input: DC Voltage (0-2V),

Display: 0 to 2.000 VDC

Resolution: 0.001 VDC

Output: RS 232 Serial interface

and also deltaT in volts connected again to another didgital indicator as specified above. Now I have been told that the com1 & com2 ports on computer can be used to send the two varities of data to the computer. But how to connect two digital indicators  to com1 and com2 ports of computer? I see only 1port of 9 pins on my CPU.I need another port too.. plz help me out.

[Henrik_Volkers]

What type of temperature sensors are used ?

For common thermocouples you would need some µV resolution.

If you have your setup running fine with the indicated display values , and you only need to read it into the PC: USB to RS232 converter are cheap...

[Buechsenschuetz]

A thermocouple sensor generates a (small) voltage, however, to measure temperature you need a cold-junction compensation circuit which usually is not integrated in standard DAQ systems. Anyhow, a resolution of 1mV is not sufficient for thermocouple measurement. It would be helpful if you would indicate which type of sensor you are going to use. 

To expand RS232 ports on your computer, there are simple USB devices with additional RS232 ports. 

[shrutimv]

I'm using a chromel-Alumel thermocouple.  I have built a circuit using AD 595 for the cold junction compensation which is tested and giving me the out in mV.  Another circuit is built to amplify delta T (differential) using INA101,which is also tested for various values of input voltages and also for higher values of gains.  Now i need to use two digital indicators of following specifications and through COM1 & COM2 port connect it directly to computer.  This part I dont understand and my CPU has only one port of 9 pins.  

Help is needed in this direction.

Digital Indicator, Mains 230V AC Operation,

Input: DC Voltage (0-2V),

Display: 0 to 2.000 VDC

Resolution: 0.001 VDC

Output: RS 232 Serial interface

[Buechsenschuetz]

OK, it seems as if you everything you need to get a suitable voltage reading. 

If you have a desktop PC you can use an additional interface card giving you 2 or even more serial ports. 

If you have a laptop/notebook you should use an USB adaptor with serial port(s). Once installed, these "look" like a serial port to the operating system and can be used as such. 

It is NOT possible to connect more than one device to one serial port, there are no splitters or multiplexers. RS232 is a true point-to-point interface not suitable for connecting several devices to one port. 

[Henrik_Volkers]

and some more stumbling blocks:

Check if the voltage module really have RS232 output ... sometimes they have a rs232 protocoll but ttl level output 3V or 5V , sometimes inverted 😮

some of these modules run mad if one sense input and digital output share the same ground .. BTDT

[shrutimv]

The output of the digital indicators are RS 232 male pins(9 pins). To one of the Digital indicators I guess I can connect a RS 232 male pin to female pin cable for feeding Delta T into the com1 port of my computer [I have only one com port on my CPU]. Since I dont have another com2 port on my PC to transfer the small voltage readings from a cold junction compensation amplifier i shall use a USB to Serial (RS-232) Adapter connected to another digital indicator, and the USB to the USB port of my CPU.  Is my understanding right?????? HELP

[Henrik_Volkers]

yes, that should work...

 start with one port and one meter for testing.