An introduction to temperature logging with a break down of the different approaches with a discussion of the various pros and cons of each approach.
Temperature logging: Why?
One of the main drivers for people embarking on temperature logging projects is legislation. Many industries have rules and regulations specifying that logging temperature is a required part of the production or storage process.
The recent legislation in the food industry specifies that the temperature must be logged in areas where there is preparation or storage of fresh fruit, vegetables, meat or fish. The regulations are governed by BRC & CMi Accreditation Standards.
Anybody involved in the storage of pharmaceuticals has a responsibility to store the drugs and medicines at an appropriate temperature under the CFR21 regulations. In addition, CFR21 also specifies that the temperature log itself must be tamper proof to ensure the validity of the temperature measurements.
In addition, many temperature logging projects are driven by a desire to perform trend analysis on the data. In heat sensitive areas, like in a server room or data centre, heat or rather the dissipation of heat, can be a major cost to the business. Consequently, it can be very useful to fully understand the heat characteristics over a long period of time.
One of the nice side effects of temperature logging is that you often get temperature alerting for free as well. Alerting can prove very useful if you need to take steps to negate the heat rise, especially in areas where the heat will rise quickly in cases of air conditioning equipment failure, like a server room.
Any temperature logging system can be broken down into two basic kinds: stand alone and automatic. An explanation of both types will now follow.
Manual Temperature Logging
A stand alone temperature logging system is the simplest, and usually, the most cost effective. Put simply, the temperature logging is performed by a data logger and requires manual intervention to periodically archive the temperature log.
Stand alone data loggers are available in two forms, blind and with a LCD screen attached. The blind data loggers have no visible means of displaying the temperature whilst the data loggers with a LCD screen are able to display the current temperature and are often able to display a simple alarm condition.
Depending upon exactly which data logger is chosen, somebody will need to retrieve the data logger from the location it is logging and take it to a PC so that the temperature log can be downloaded to a PC. The data logger is then reset ie the temperature log is cleared and replaced into the location where it will continue to log the temperature.
Typically, a data logger can log up to 2-3000 temperature readings which means that the intervals for downloading the temperature log can be reasonably far apart. Though, it is not recommended that the log downloads are too far apart because if the data logger is lost or stolen then all of the data for the intervening period will be lost. Lost data may be hard to explain away during an audit.
There are systems that negate the requirement to perform manual archiving of the temperature logs, these will be discussed next.
Automatic temperature logging
Automatic temperature logging systems do not require manual intervention, instead they periodically log the temperature themselves. This has the considerable benefit of reducing the amount of work required to run a temperature logging system.
In addition, larger temperature logging systems, usually using environment monitors, can be constructed that are able to measure the temperature in many separate locations, even locations that are widely geographically separate. Of course, the downside is that a widely dispersed system is likely to depend upon a computer network, and as such, will only work when the network is operating correctly. This is generally not a problem as modern networks tend to be pretty resilient.
One relatively cost effective solution can be to use a PC based solution. You can purchase either USB, serial or network based thermometers, and together with some suitable software (like Intellipool), you can turn a spare PC into a sophisticated temperature logging system.
Of course, automation does come at a price, an automatic temperature logging system can cost substantially more than a manual system.
One of the side effects of building an automated temperature logging system is that often you get temperature alerts as a free side effect. Systems based upon the network can utilise email services to tell you in a timely manner when the temperature has gone out of acceptable bounds. In addition, SMS messaging is available as an add-on for a number of systems too.
One factor to keep in mind when building your temperature logging system is the importance of data backup, especially if the system is being constructed for regulatory compliance reasons. Any system based around a PC can be integrated into your existing data backup regime. Data residing on the PC can either be backed up remotely via a drive share, or the data can be backed up onto a server drive and backed up as a regular part of the server's backup regime. Temperature monitors, though they are completely stand alone, also need to be backed up periodically. Whilst they are generally pretty reliable, any failure will result in the complete loss of all of the temperature logs stored on the device. Most units can have their temperature logs downloads to a PC for backup purposes quite easily. You also need to check whether the environment monitor is in fact storing the temperature logs inside none volatile memory. Plainly if it is not, then a simple power cycle will result in the loss of all of the temperature logs.
Precisely how you design your temperature logging system depends upon a lot of different requirements. If your requirements are quite simple and extend to only a few locations then a simple manual temperature logging system will likely suffice.
If on the other hand you have pressing temperature alerting requirements, or have a number of locations that must be monitored, then a manual system may not be suitable. An automated temperature logging system will pay dividends when your requirements stretch to a number of different locations and you have an alerting requirement. Automated systems tend only to be as good as the network they are required to use. So, if your network is unreliable, it may be wise to invest in upgrading your network to be more reliable. An automated temperature logging system running on an unreliable network will result in an unreliable temperature logging system.