4.3.12 EEPROM Write Frequency Warning E2.Fr

As stated in sections 8.3 and 8.4 the EEPROM used in the 800 range has a limited number of write cycles. If any parameter writing to the EEPROM (typically over digital communications) starts to approach the limit specified for the EEPROM, an advanced warning alarm is activated. The alarm is displayed in a similar manner to other alarms. It consists of the mnemonic E2.Fr, followed by an identifier of the first parameter that has caused the warning. This is flashed in sequence with other active alarms in the second line of the display. The identifier is the parameter Modbus address (Hex), for example, E2.Fr, flashing in sequence with 00B1 identifies the Alarm 3 threshold parameter.

 

Should this alarm occur, it is essential that the parameter(s) identified are removed from the communications and, where possible, substituted by alternatives such as those stated in section 8.4 – ‘EEPROM Write Cycles’. In the unlikely event that the identifier shows an address of Hex 4000 or above, this indicates that an internal parameter has exceeded the write rate and you should contact your supplier.

 

The calculation for the warning to be displayed is based upon a worst case write cycle of 100,000 over a 10 year minimum life span.

 

The hourly write rate to give a minimum 10 year life is calculated as follows:

 

10 year rate = Worst case life cycles / the number of hours in 10 years

= 100,000 / (10 * 365 * 24)

= 1.1 writes per hour

 

When configuring, commissioning or starting/completing an operation it is conceivable for the number of writes to be greater than this rate. However, as this is not expected to continue for a long period, the warning will not be activated until a period of 6 hours has elapsed. The 6 hour check is overridden if the number of writes in a single hour is greater than a maximum threshold. This threshold has been set at 30 writes i.e. one every 2 minutes. This is to help conserve EEPROM cell life by informing the user early of a potential issue.

 

Notes:

1. It is possible that during commissioning or development of a program a valid parameter is written to repetitively. This may cause the warning message to be displayed and under these circumstances it may be disregarded. If preferred, the message may be reset by power cycling the instrument. The warning must not be disregarded, however, if it appears during normal operation and the root cause must be identified.

 

2. For the main control set-point only, the 100,000 write cycles figure is increased up to one million by spreading the set-point writes to the unused memory locations.

 

Because it is not possible to predict the writing frequency to the set-point parameter, the EEPROM Write Frequency Warning E2.Fr message will be disabled for this parameter only.