STAN S31 CMS interconnection guide

This guide is intended to provide basic installation and troubleshooting instructions for connecting a STAN S31 fetal monitor to a 3’rd party Central Monitoring System communicating over RS-232.

In case you need to contact technical support during installation and troubleshooting, please have the following information ready

  • Fault description, what steps have you tried and which step is failing.
  • Brand and revision of Central Monitoring System.
  • Type of wall connector (manufacturer, article numbers etc.)


Most CMS manufacturers supply wall boxes to facilitate an easy connection between the CTG monitor and the CMS. The general rule is that the internal routing of these wall boxes is proprietary information owned by the CMS manufacturers. In general, CMS vendors provide cabling for all common CTG monitors on the market and the recommendation from Neoventa is to acquire cabling from the CMS vendor. As a service, Neoventa also works with the CMS manufacturers with the ambition to provide cabling but the availability of these may vary between CMS brands.

In case cables need to be adapted on site, the routing of the STAN connector is described in PRD101004/44, STAN S31 Service Manual.

Important to note is that the connector on STAN S31 that is used for CMS communication (COM2) does not provide electrical isolation. Therefore, an isolation device is needed between the COM2 port and the CMS server. For this purpose, Neoventa provides an RS-232 Isolation kit (article number CNK101005/1). Note that some wall boxes provide this electrical isolation in which cases the Neoventa isolation kit is not needed. Examples of isolated wall boxes are the ones from CMS manufacturer Medexa, for their Milou CMS.

Step by step interconnection guide

1. Start by connecting the acquired CMS cable between STAN S31’s COM2 port and the CMS connector without the RS-232 isolation kit in between.

2. Start the STAN S31 and enter the service settings. Change the SURVEILLANCE_PROTOCOL setting to either CTG Protocol (COM2) or STAN Protocol (COM2), depending on whether your CMS supports the display of ST information or not. (The CTG Extended Protocol (COM2) and STAN Protocol R1A (COM2) settings may be required for legacy CMS versions.)

3. Start a new recording. Connect e.g. a TOCO to STAN. There is an indicator ‘Central Monitoring’ in the lower left corner of the screen that is initially red but should change to green within seconds. Indicator becoming green means that the communication is setup correctly. Check the screens of  the CMS to see that the STAN recording is displayed correctly. Then continue with installing the  RS-232 isolator kit according to instructions below.


4. If the Central Monitoring indicator stays red the communication with the CMS fails.
a) Troubleshoot by first crosschecking with another CTG monitor, preferably of another brand, to ensure that the wall connector and the cabling to the CMS Server are working correctly.
b) Some legacy CMS may require the CTG Extended Protocol (COM2) and STAN Protocol R1A (COM2) setting, so if you have an older CMS version, you may want to try a few other settings of the SURVEILLANCE_PROTOCOL parameter.
c) Some CMS, especially local variants in the US, only allow their systems to communicate with CTG monitors explicitly validated by the CMS manufacturer. If you suspect this may be the case with your CMS, please contact the CMS vendor to confirm that their system is validated with Stan S31.
d) Also crosscheck in another room with another wall connector. Sometimes the cabling between wall connector and CMS server is too long to drive the circuitry in the CTG equipment. Normally for RS-232 cabling, 20 meters is the maximum cable length without repeaters or other types of amplifiers.
e) Also ensure that the wall connector is for RS-232 connection (compared to Ethernet, RS- 422/RS-485 etc.).

5. If steps a) to e) above did not solve the problem, it is likely that the problem is in the cable itself. Contact the cable manufacturer for support. If you are building the cable yourself you may want to check that the configuration of the Rx/Tx lines is correct. Some wall boxes are built for straight Rx/Tx lines and some require them to be crossed. An easy test can be to test with an extra null modem plus gender changer.

Installing the RS232 isolator

6. If the Stan S31 and the CMS are communicating properly, continue with connecting the RS-232 isolator kit. Note that this is not necessary if your wall box has built in isolation. To install the isolator, follow the instructions provided with the kit. It is important that the isolator is configured in the right direction, i.e. DTE/peripheral facing the Stan side and DCE/PC facing the CMS side.

7. Start a new recording on STAN and verify that the Central Monitoring indicator in the lower left corner turns green within a few seconds. If it stays red, the communication with the CMS fails.
a) Double-check that the isolator is connected in the right direction, i.e. DTE/peripheral to the Stan side and DCE/PC to the CMS side. You may also want to open up the isolator box, to double-check that the jumper settings are correct from factory, i.e. DTE on the Stan side and DCE on the CMS side. (See description and pictures later in this document.)
b) If the communication fails when you use the isolation box, it may be so that the CMS side requires DTE configuration. Open up the isolation box and move the two jumpers on the CMS side from DCE to DTE. Do not forget to disconnect the box from both STAN and CMS first. Note that the Stan side should always be in DTE configuration.
c)  If changing the CMS side configuration from DCE to DTE does not solve the problem, it is likely that the Rx/Tx lines from the CMS side is not of sufficient power to drive the isolation box circuitry. This can be tested by looking at the LEDs on the isolator’s circuit board while the device is being used. The LED on the CMS side should blink with regular intervals. (This interval is CMS dependent, but the CMS should poll for connected CTG device at least once in 15 seconds.) If the CMS side LED does not blink in 60 seconds and the communication is not up- and-running, it is likely that the Rx/Tx lines from the CMS side do not provide enough power to drive the circuitry. If this is the case, the solution may be to use a variant of isolation box that is driven by an external power source. (Note, the LED on the STAN side will blink once right when a new recording is started, but will not blink again until the communication with CMS is up and running.)


Brief description of the RS232 isolation box

The isolation box is built so that you can use two different types of settings. The Isolation box is pre- configured DTE (Stan side) to DCE (CMS side) from start but sometimes you may need to use the DTE to DTE configuration.



You can open the isolation box by use of a screwdriver or similar on the four corners of the box.


Inside the box you will see four jumpers, two controlling DTE/DCE configuration on each side.


Inside the box you can change the internal jumpers on the CMS side to DTE instead of DCE. It is also recommended that you mark the box with ‘Internal jumpers changed’ or ‘DTE to DTE config’ for future purposes.


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