Temperature montoring systems. Which is better; manual, mechanical or electronic?

The need to monitor and document temperature or has never been
greater in the history of mankind. Over 70% of all measurements
of process variables are of temperature. Many if not most
products and manufacturing processes are temperature sensitive,
or temperature critical. 

Because the quality and safety of so many products is dependent
on temperature it has been become, not only crucial, but even
mandatory that temperature be monitored during the
manufacturing, storage and transportation phases of many
products life cycles. Private certifying agencies and government
regulations are requiring an increasing number of products to be
temperature monitored and documented.

There are basically three ways to monitor temperature; manually,
mechanically or electronically. 

Monitor temperature: The manual method

The manual way is the least accurate and would appear to be the
least expensive. It is actually the most expensive but the costs
are hidden so that they aren't noticed as much. An employee
assigned to periodically check and record the temperature may
only need five or ten minutes a day to record the temperature
but that can add up to over 50 hours a year if he is only
recording the temperature once a day. Even if the employee is
paid minimum wages this can amount to over $ 500/year once you
add in employee perks and wasted time to get a pencil, change
and file the temperature record, etc...

Monitor temperature: The mechanical method

Recording time mechanically requires a chart recorder. This
device is more accurate than the manual method. It draws a line
on a paper chart to show a temperature history over a day, week,
or month, at which time the chart must be replaced with a new
one and the old one filed away. The chart recorder is even more
expensive than the manual method, since it requires employee
labor to change the chart and pen periodically and you have to
buy the charts and pens. The chart recorder itself can cost
between $ 300 and $ 1200, while the charts and pens can add an
additional $ 50/year. On top of all this you still have several
hundred dollars of employee time.

Monitor temperature: The electronic method 

The most accurate and least expensive way to document
temperature is with a data logger. Data loggers come with or
without an LCD display. The display is useful if you need to
monitor the temperature and not just document it. Data loggers
without a display must be programmed by wiring them up to a
computer. 

Data loggers are programmed to sample and store temperature
electronically, after which they can be downloaded to a computer
to generate a printed record to be reviewed or filed away. The
initial cost is less than the chart recorder and the collected
data must be downloaded only once every few months so there is
really no ongoing maintenance or consumables to purchase.

The chart below compares some of the features of the three
methods of monitoring and/or documenting temperature.