Warning: Resetting a high set point inhibit will not cause an
alarm to occur if the Process Value does not first drop below the
high set point value. Do not use the Set Point Inhibit feature if a
hazard is created by this action. Be sure to test all combina-
tions of high and low set point inhibit actions before placing
control into operation.
Options and Non-volatile Memory
There are many different types of memory used in computer driven devices. The
terms RAM (random access memory) and ROM (read only memory) are a couple
with which you may be familiar.
RAM is used in computers to run programs and hold data for a short period of time.
This is the memory that is used primarily in PCs. RAM is very fast and can be read
and written to over and over again.
ROM is used in computers to hold the ‘permanent’ programming that allows a PC
to start. This memory is ‘burned in’ to the chip itself and can not be changed. Unlike
RAM, however, this memory is permanent. While it can not be changed, it can not
lose its programming when power is turned off.
There is a third type of memory that is now currently used to combine the character-
istics of both RAM and ROM. This is known as EEPROM (electrically erasable pro-
grammable read only memory). While the name may be long and somewhat cryptic,
the EEPROM can be erased and re-written many times, and yet hold the pro-
grammed data even over long periods of time when the power is off. This is the type
of memory that all Omega products use to save the settings your program in your
control. The reliability and longevity of the data retention is what allows us to guar-
antee a 10 year data retention without power.
In normal operation, the control uses RAM, just as any other computerized device.
Whenever you make a change to one of the parameters in the control, the set point
for example, the new value is written into the EEPROM. This way, if power goes off
for whatever reason, when power resumes, the latest settings are preserved. When
power is turned on, the data is copied from the EEPROM to the RAM to begin oper-
If EEPROM is such a wonderful thing, you might ask, why bother with RAM? One
reason is that RAM is much faster than EEPROM. Faster speed gives you better per-
formance in critical control functions.