EBME Forums Forums Maintenance Test Equipment About Timeter RT-200

I recently obtained some information about the RT-200 RS232-C communication interface converter board, and I'm sharing it here for anyone who might be interested.
There is no clue yet about the software that matches the RS232-C communication board. If anyone has a matching online software, please feel free to contact me. Thank you

Do you have the instrument in your possession? The RS-232 format should be well known. If you have access to the RT-200, what are you getting as output(s) on J1?

I notice that J-2 remains blank. I'm surprised that the interface board only supports J-1 (the RS-232 connector); which is a pity as there is a lot of info on the GPIB (General Purpose Interface Bus) on line. I believe that the GPIB is a parallel format.

The picture was taken by a Canadian seller on eBay; only his RT-200 main unit has an RS-232C interface on the back.(https://www.ebay.com/itm/1879982158...338722076&customid=&toolid=10050)
This is the only RT-200 host I can currently find with an RS-232C interface output.So I had him take pictures of the internal motherboard.
The markings on the chips on his RT-200 motherboard were intact and had not been erased.


My own RT-200 main unit doesn't have this kind of signal adapter board, meaning J3 and J4 are empty, and expansion ports NO1 and NO2 are also empty.

It seems that some software is needed to interface with the J-1 port, but I haven't found any information or clues related to that software.(It looks like a printer interface, meaning it can only output signals.)
Frankly, I have never seen an RT-200 mainframe with a GPIB interface.

I've been looking for how Timeter calibrates the RT-200.Because the U1-U6 EEPROM chips on the RT-200 motherboard are UV-erasable EEPROM chips.In other words, it is read-only and the data cannot be modified in real time.?Unless they test it once, then remove the chip, erase the data, rewrite the new data, and then reinstall and test it again.?

I'm hoping that someone somewhere shall be able to provide "chapter and verse" on the GPIB of the RT-200. Surely GPIB must have been used as it lends itself more usefully to instruments such as the RT-200 ... that is, for data logging purposes.

I'm guessing that RS-232 would be more useful when recording varying output values. But I am wondering if the RS-232 facility could also be for inputs to control the RT-200 ... remotely, for example. I'm wondering also if both interfaces ever appeared on a RT-200 (and could this indeed even have been possible .. seeing as how close together the J3 and J4 connectors are).

I notice from your images the DIP switch on the serial comms board (as would be expected for setting up protocols) and also that the board is plugged in at J4 on the main board. Perhaps J3 is for the GPIB.

I have been unable to find any information regarding either interface. But someone must know.

Lastly, need I remind you that the old (May 1988) RT-200 manual makes clear that U1-U6 ... "Do not remove EPROMs unless instructed by factory"! Notice also that (in the images you have provided) the EPROMs are marked by hand with the instrument serial number.

This is a clear picture of the interface circuit;

it appears that it requires computer software to function.

I spent a long time repairing the flow module section of this RT-200 gasflow analyzer (RT-203M).
Today is the time to summarize the situation. I have completed the initial calibration and conducted verification tests for low flow rates; high flow rates have not yet been tested, but I anticipate there shouldn't be any major issues.

Let me describe the sequence of events from the beginning.
The main issue with my RT-200 unit is zero-flow drift in the RT-203M gasflow module.
The specific symptom is as follows: after connecting the power, entering the function code, pressing Enter to access the test mode, and pressing the zeroing button, the display shows "0.00 LPM"; however, the flow rate reading changes significantly over time, even though no airflow is entering the high-flow or low-flow test ports.
Enter the "30" function test code and press the Enter key; you will see the displayed number changing slowly.
In other words, it is not possible to achieve the stable display of the voltage value corresponding to "385" (±0.005 VDC) as described in the manual.
I ultimately discovered that the zero-point drift was caused by the aging of the 125PC05D1 pressure sensor.

The 125PC05D1 is an older model of differential pressure sensor; it has been discontinued, and an identical replacement model is no longer available on the market.
I reverse-engineered the original signal modulation board and found that R1123 (VBSET) is used to adjust the pressure sensor's sensitivity; R1116 (ZERO) is used to zero the sensor's S+ or S- terminals relative to GND; and R1111 (XDBAL) is used to zero the offset between the sensor's output pins, S+ and S-.R1102 (NULL) is used to adjust the final analog output voltage.


At a bias voltage of 10.0 V, the sensitivity of the 125PC05D1 pressure sensor is 70 mV/5 psi (14 mV/psi) or 2.0 mV/kPa.
The gain of the original signal modulation board is vo/vi = (1 + (2 × 24,800 / 100)) = 497.
Therefore, the sensitivity of the original module is 2mv/kpa × 497 = 994 mV/kPa.

I selected the XGZP192-010G as the new replacement pressure sensor.The sensitivity of the XGZP192-010G pressure sensor is 4 mV/kPa.If the XGZP192-010G is used, the instrumentation amplifier circuit in the original design requires a gain of 994/4 = 249.
At the same time, resistor R1101 needs to be replaced, changing its value from 100 ohms to 200 ohms. Since the REF01 is a 10.0V voltage reference chip, the optimal condition is for the actual bias voltage to be slightly below 10.0V; therefore, I set R1101 to 195 ohms.At the same time, resistors R1118 and R1113 need to be changed to 24k and 27k.Only in this way can the new XGZP192-010G pressure sensor operate at its optimal performance level.

It is currently functioning properly. Although the original signal circuit utilizes standard OP11EY and LM346N operational amplifiers to form the instrumentation amplifier stage, the temperature drift is minimal.

I have the LT1014 instrumentation op-amp chip on hand; would replacing the OP11EY and LM346N with the LT1014 yield better performance?

I am attempting to build an upgraded signal conditioning board using a 0.1% precision pressure sensor paired with a PGA chip; if anyone is interested, please contact me. I plan to release the design in the hope that it assists current RT-200 users or those looking to calibrate the device. I look forward to everyone sharing their insights.

Best regards

I applaud your inspirational skill, tenacity and perseverance.