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What are the proper communication port settings for connecting a 3000 series analyzer to a computer through the RS-232C port?
What are the pinouts for the RS-232C port on 3000 series analyzers?
Is the RS-232C communication port periodically sending data to the computer?
Before receiving data, should the computer send an emission request to the analyzer?
Immediately after the initialization phase, should the computer send the analyzer the -st- command and then wait to receive the data?
What is the sequence to put an analyzer in calibration mode and to exit out of it?
What is the maximum cable length for an RS-232 communication port?
Description for setting the RS-232 data link.


What are the proper communication port settings for connecting a 3000 series analyzer to a computer through the RS-232C port?

Parameter
Setting
Baud
2400
Data bits
8
Parity
none
Stop bits
1


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What are the pinouts for the RS-232C port on 3000 series analyzers?

Teledyne's 3000 series analyzers have a 9-pin D connector. The mating connector pins are numbered as in the following diagram. The diagram shows the locations of the pins of a male connector as viewed from the front (the 3000 series instruments presently have a female connector).


Only 3 pins are required for proper communication, they are:

Pin Number
Name
Description
2
RXD
Receive pin (connects to the TXD pin of the second device)
3
TXD
Transmit pin (connects to the RXD pin of the second device)
5
GND
Ground pin (connects to the ground pin of the second device)

The proper connections between the analyzer and computer can be made by using a straight through cable. To make this cable, connect the TXD pin from the analyzer to the RXD pin of the computer. Connect the RXD pin from the analyzer to the TXD pin of the computer. Connect the GND pin from the analyzer to the GND pin of the computer.

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Is the RS-232C communication port periodically sending data to the computer?

When the 3000 series instrument is turned on, it sends a heading through the RS-232 that reads something like this:

Teledyne Model 3000T Oxygen Analyzer


It will send nothing while the instrument is in the self-diagnostic mode, collecting electronic zeroes, while in span mode, and while on the zero mode. In the sample mode, a stream of data is sent every two seconds and it looks like the following text string:

ST, 0.00 PPM, RA-LO 0-100 PPM, AL-1 DISABLED, AL-2 ON, (CR)


The above stream of data is interpreted as follows:

ST means start

0.00 is the oxygen concentration

% or PPM is the unit of concentration

RA means the instrument is set to auto ranging / RF means the instrument is set in a specific range of interest. The range the instrument is on follows: LO, MED, HI, or CAL

0-100 PPM is the setting for the LO range, (0-100 PPM is factory default for the LO range but can be set as low as 0-10 PPM)

Alarms that disabled or tripped end the text string
AL-1 DISABLED means that alarm 1 has been turned off or disabled
AL-2 ON means that alarm 2 has been tripped
If there is no message about either alarm 1 or alarm 2, it means that the alarm is not disabled but has not been tripped

Carriage return is at the very end to start a new line

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Before receiving data, should the computer send an emission request to the analyzer?

No. Whether the RS-232 is connected or not, the analyzer will send a stream of data after the analyzer is turned on. The computer must be properly setup as explained in the manual to receive the data.

The only way to stop the analyzer from sending data out is sending the ‘st’ command. It is case sensitive and must be followed by a carriage return (CR). Once that happens, the only way to get the data from the RS-232 is to type the ‘st’ command again.

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Immediately after the initialization phase, should the computer send the analyzer the -st- command and then wait to receive the data?

No. Once the instrument is turned on, data is sent every two seconds regardless of whether a RS-232 monitor is connected to the analyzer or not. First, initialize the computer with the appropriate parameters. Second, plug the analyzer into the computer. Finally, turn the analyzer on.

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What is the sequence to put an analyzer in calibration mode and to exit out of it?

No. Once the instrument is turned on, data is sent every two seconds regardless of whether a RS-232 monitor is connected to the analyzer or not. First, initialize the computer with the appropriate parameters. Second, plug the analyzer into the computer. Finally, turn the analyzer on.

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What is the maximum cable length for an RS-232 communication port?

For the original RS-232 standard, the cable between the driver and the receiver was specified for a maximum of 15 meters in length. This part of the standard was changed in a revision to a maximum capacitive load of 2500 pF. The maximum cable length is determined by the capacitance per unit length of the cable which is provided in the cable specifications.

The total capacitance is approximated by the sum of the mutual capacitance between the signal conductors and the conductor to shield capacitance (or stray capacitance in the case of unshielded cable).

Cm = Mutual capacitance between conductors.
Cs = Conductor to interface cable shield capacitance (if shielded cable is used) - 2*Cm
or stray capacitance to earth (if unshielded cable is used) - 0.5*Cm.
Cc= Cm+Cs = Total capacitance per unit length

Example: Assume the user has decided to use non-shielded cable when interconnecting the equipment. The cable mutual capacitance (Cm) of the cable is found in the cable’s specifications to be 20 pF per foot. Assuming the capacitance of the receiver is too small to consider and using the equation of the figure above:

Cc = 20 pF / foot + 0.5*20 pF / foot
Cc = 30 pF/ foot

The maximum cable length then becomes:

Lmax = (2500 pF) / (30 pF / foot)
Lmax = 83 ft approx.

If a longer cable length is required, the user would need to find a cable with smaller mutual capacitance.

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Description for setting the RS-232 data link.

Click for a procedure in PDF format.

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