Signal Boxes that have been send back to repair may have an old version of PLC code loaded.

How do I check/update the PLC code after replacing the Signal Box? See long description. PLC Code version not updating in the field Issue : PLC code version does not update to the latest version when a signal box is installed in the field during a field replacement procedure. Scope : This issue is specific to the DVMR platform which uses the 5161931 Heat Exchanger Cabinet (HEC). The scope is contained to systems using a signal box FRU (P/N 5269691) that previously was in the field and was repaired by the vendor and put back into service as FRU stock. Summary : The MR system exchanges command and feedback signals with the programmable logic controller (PLC) in the HEC signal box via Ethernet and serial communication paths. The PLC operates on a Unitronic’s (vendor) operating system and has custom-written code running on it to execute the cooling control required of the HEC. This code has been modified several times during production of DVMR systems to fix problems and account for hardware changes as a result of cost-reduction projects. Upon the first connection of a PLC to an MR system via Ethernet, the MR SCP will look at the values stored in the PLC’s “MI 4” and “MI 5” registers. These ‘memory integer’ addresses store checksum values that are unique to the PLC code version. If the checksum values in these registers do not match the values stored on the SCP, the MR system will initiate a download of the PLC code that is stored on the MR system. If, however, the checksum values on the PLC match what it in the MR system, there will be no forced code download. An important thing to understand about MI 4 and MI 5 is that they are not internally-generated values in the PLC. The checksum values are communicated FROM the MR system and stored TO the PLC. For example, a HEC running stand-alone without ever having been connected to an MR system will have a zero-value for both MI 4 and MI 5. Once hooked up to the MR system, the checksum values are generated and the MR system writes these values to the MI 4 and MI 5 addresses. Where this behavior becomes an issue is when a signal box has previously been in the field and failed, thereby going through a repair process at Lytron and put back into FRU stock for a future spare-part need in the field. Lytron’s repair process for a signal box includes downloading the G3.02.16.2009 version of PLC code that is specified in the 5161931PSP. The values stored in flash memory for MI 4 and MI 5, however, do not reset during this code download. When this signal box arrives now arrives at a site, the MR system reads the MI 4 and MI 5 addresses and sees that the checksum values are correct (they match what is on the MR system). Therefore, the MR system does not force a code download and the HEC is operating with G3.02.16.2009 version of code instead of the proper G3.08.25.2009 version. Impact : The impact of running a HEC with code version ‘G3.02.16.2009’ instead of ‘G3.08.25.2009’ is low-risk. The change between the two versions was to address the speed at which the Chilled Air Temperature reaches setpoint after completing TPS reset on a 450w system. Once setpoint is achieved, the MR system performs as specified. It is simply an elongated transition time from completing a TPS reset to when the chilled air temperature comes into allowable range. There is no impact to the performance MR750 or MR450 products that might be running the G3.02.16.2009 code version. To reiterate: the only impact is to the length of time in which it takes an MR450w system to achieve chilled air temperature setpoint after completing a TPS reset, and that particular system would need to have installed a signal box from FRU stock that had been through the repair cycle at Lytron.