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Remote Temperature Sensor - How to Choose One
Remote temperature sensor technology will help you to keep equipment at your remote sites online when they otherwise would've failed due to overheating or (less commonly) severe cold.
Temperature sensors are important whenever you're working with computer equipment. Computers generate large quantities of heat as they operate, and that heat must be managed through cooling or forced ventilation to prevent thermal shutdowns.
Remote temperature sensors are unique in that they allow you to monitor temperature across town, across the country, or across the globe. Since direct viewing of the temperature reading is obviously impossible with such range, remote temperature sensors transmit their temperature reading in one of a few different methods. If you have just a few remote temperatures to monitor, you can configure your remote temperature sensor to send you an e-mail, text message, or phone voice message. The advantage of this direct approach to temperature notifications is that no other equipment is required.
This remote temperature sensor has a visible meter if you happen to be at the site, but it also transmits temperature data back to you.
If you have more than a handful of remote temperatures keep track of, however, you'll benefit from using a central master station to collect many temperature readings simultaneously, aggregating them into one display, then sending you e-mails or phone messages as needed for the most important temperature situations.
It's important now to clarify a bit of technology for you. Although I've referred to a remote temperature sensor so far as a single device, I've actually been referring to a combination of two boxes that work together to provide remote temperature notifications.
The first key component of any remote temperature sensor system is the temperature sensor itself. In industrial environments, these are most commonly powered by +12 VDC. If you have sites that run on either 110 VAC or -48 VDC, you can create +12 VDC using wall transformers. There is, however, a much better way to power your sensors that eliminates the need for wall transformers.
Whether you have this sensor power advantage depends on your selection of an alarm remote to collect data from your temperature sensor(s) and send it back to you. An alarm remote is a small box that you deploy at your remote site to provide intelligence for multiple "dumb" sensors. Alarm remotes are most commonly powered by -48 VDC, so they're convenient to install at remote sites that run on protected battery power.
The best alarm remotes for remote temperature monitoring provide an onboard +12 VDC power supply. This eliminates a whole lot of wiring headaches, as you don't have to run a separate power feed (and somehow convert to the required +12 voltage) from the wall.
Alarm remotes vary in the number of sensors that they can accept. Your choice should depend on the number of distinct temperature measurements you need to make at a single remote site, but understand that you do have a choice.
Alarm remotes connect to remote temperature sensors in one of two ways. First are discrete inputs, which are also called "digital" or "contact closure" inputs. These simply detect whether a connected dry contact is open or closed. While these inputs are simple and inexpensive, they do limit your choice of temperature sensors to discrete sensors only.
Discrete temperature sensors cannot tell you a precise temperature value. Much like you might set your thermostat in your home, you'll need to pre-specify a specific temperature boundary when you're setting up your discrete temperature sensor. When this temperature threshold is crossed, your discrete temperature sensor will latch/close its internal contact closure. This will be detected by your alarm remote, triggering an automatic alert back to either you or your central office.
Let's say that you set your discrete temperature sensor with a threshold value of 85 degrees Fahrenheit. If the closure is latched (meaning "active"), you know the temperature is above 85 degrees. You don't know, however, if it's at 86 or 186. There's no way to gauge the scope of the problem.
Fortunately, there is a superior technology for measuring temperature. You'll be able to leverage it if you select an alarm remote that has one or more analog inputs. An analog input, in most cases, measures a precise value between 0-5 volts DC or 4-20mA. The best analog inputs can be toggled between these two standards using a simple hardware DIP switch.
Unlike with the discrete remote temperature sensors I mentioned earlier, analog sensors are able to return a highly accurate value (usually within 1 degree of the true site temperature). This means that, at any time, you can check the temperature at your remote site. If you receive an alert that the site temperature has exceeded 85 degrees, you'll know whether it's 86 or 87 or 88 or 186.
Let me take a minute to explain how alerts work with analog temperature sensors. Since analog measurements are based on a continuous range of values, it may not be initially apparent to you how analog sensor can trigger threshold alerts. In this situation, you are correct to assume that your sensor will not output discrete threshold alerts to your alarm remote at the site. Instead, you'll be leveraging the built-in intelligence of your alarm remote. Any respectable alarm remote, at minimum, will support at least two software threshold temperature alerts. This is the minimum acceptable number of threshold values because it allows you to specify one "too high" and one "too low" value.
As you can see in this example, a web interface to display temperature levels on animated analog gauges makes for highly intuitive remote temperature sensing and, when necessary, response.
Superior remote temperatures sensor systems will have even more supported threshold values. Ideally, you'll have four configurable software thresholds. This allows you to specify both major and minor variants of high temperature and low temperature alerts. While a minor high-temperature might warrant continued monitoring and a routine response, a major high-temperature should generally trigger an emergency response to prevent thermal shutdowns and expensive equipment damage.
Review of Today's Remote Temperature Sensor Equipment:
No review of remote temperature sensors would be complete without reviewing the current state available technology for remotely monitoring temperature.
First, let's start by looking at a small remote designed for light industrial telecom and IT scenarios. The TempDefender IT is a very compact alarm remote with a highly specialized sensor interface that simplifies wiring by communicating with and powering multiple remote sensors over one wire.
The TempDefender has four "D-Wire" sensor inputs that supported grand total of up to 16 remote temperature sensors (of course, other sensors like humidity sensors are available if you'd like to monitor other things at the same remote site). How can this alarm remote support four times more sensors that it has ports? The specialized sensors of the TempDefender have both "in" and "out" ports, so they may be daisy-chained together from a single alarm remote input port.
If you'd like to receive automated voice messages on your phone when your temperature exceeds a threshold value, you will need to choose an alarm remote that has the capability. One good small remote that has this capability is the NetGuardian LT. Simply by plugging in a phone line and configuring your phone number(s), this small NetGuardian will call you whenever you have an important temperature alarm. The voice is synthesized, so there's no need to laboriously pre-record each alert message beforehand.
If you have a lot of remote temperature sensors (plus other telecom equipment and environmental values to monitor), you should consider a larger RTU like the NetGuardian 832A. It has 32 discrete inputs and 8 analog inputs, so you can monitor a variety of sensors. Plus, the other input not used with external sensors can be used to monitor equipment alarms (any device that outputs a contact closure), power input voltage, or battery levels (by monitoring voltage drop).
When it's time to select the actual external remote temperature sensor hardware you will deploy with your alarm remotes, it's best to use sensors recommended by a trusted alarm remote manufacturer. How do you know who to trust? One way is to examine the build quality of alarm remotes. A solid build (high temperature tolerance and a metal chassis, especially one that's powder-coated for corrosion resistance) indicates two advantages.
First, the manufacturer that built it knows what they're doing. They understand remote monitoring, including remote temperature monitoring, and they have enough experience to recommend a remote temperature sensor that will work well for your project and survive in your site environment.
Second, they will only recommend sensors that are as reliable as their remotes. To do otherwise makes no sense. Why recommend an accessory that won't last as long as the master device it's attached to? So, by assessing the quality of a company's alarm remotes, you will understand their ability to recommend temperature sensors for remote temperature monitoring.
I hope that you've found this introduction to remote temperature sensors useful. Please review the links below for more equipment recommendations and information:
Related Topics:
Remote Temperature Monitoring
Network Temperature Sensor
Related Products:
- Remote Temperature Sensors, Humidity Sensors, and other sensors
- Vaisala - Temperature/Humidity Sensor
- NetGuardian 832A (Large RTU to support multiple temperature sensors and other equipment alarms)
- TempDefender IT (Compact alarm remote designed for server rooms and data centers)
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