If you are responsible for managing a remote site, it is important to choose the right humidity detector to help you monitor the environment. The wrong choice can lead to decreased accuracy and reliability, and even put your site at risk.
There are many factors to consider when choosing a humidity detector, including its sensitivity, selectivity, accuracy, and remote monitoring capabilities.
When choosing a humidity detector for your remote site, it is important to consider all of these factors to ensure that you choose the right device for your needs.
Sensitivity, formally defined, is the ability of the humidity detector to measure small changes in humidity.
Obviously, your need for this varies based on the application. For general telecom huts that I work with a lot, there's really not a tremendous need for humidity accuracy. In fact, some people I work with monitor room temperature religiously (ex. not with just a simple digital thermometer) but don't much care about humidity. Climate tends to be the factor that determines whether humidity needs to be monitored.
In short, if you're monitoring a remote telecom hut of some kind, any humidity detector with accuracy within a few degrees of relative humidity (RH) should be fine.
The situation changes a lot if you're monitoring something more sensitive, like dry goods, food, or medical supplies. Measuring water vapor in the atmosphere for the calculation of the dew point requires high sensitivity for aviation safety. In that case, a few degrees of humidity can make a big difference in safety and efficacy.
Accuracy is the degree to which the humidity gauge measures humidity levels accurately. This is distinct from sensitivity.
Imagine that you have a humidity detector that has high accuracy but limited sensitivity. It might very reliably measure temperature, but only to the nearest 5 degrees.
A humidity sensor with higher sensitivity might detect changes down to 0.1 degrees, but that barely matters if it doesn't have the accuracy to back that up. A reading like "80.3% RH" does little good if the correct reading should be 50%.
Remote monitoring capability is an important consideration for any remote site manager.
A humidity detector with remote monitoring capability can send alerts to a central location when humidity levels change, so that you can take action to maintain a safe, comfortable, and/or "in spec" environment for your site.
Classically, a humidity detector can latch a contact closure or return a variable voltage/current to report its reading to an on-site RTU (Remote Telemetry Unit or Remote Terminal Unit).
That device will then send the reading to your central server or SNMP manager using some kind of protocol (SNMP is very common). In smaller systems, you might have your RTU send you email or SMS directly.
If you don't already have an RTU at your remote site, you'll need to choose one that is compatible with the humidity detector you select.
RTUs come in a wide variety of shapes and sizes, with different feature sets. They can be very simple devices that just take readings from sensors and report them to a central location, or they can be much more sophisticated devices with digital displays that allow you to configure alarms, take corrective action, and so on.
When choosing an RTU for humidity monitoring, you should consider the following factors:
Make sure the RTU speaks the same protocol (or electrical communication like closures/voltage/current) as the humidity detector. SNMP is very common, but there are others. Some manufacturers of RTU also sell their own brand of bus-powered humidity sensors, which can be very convenient.
You'll need at least one input for the humidity detector, but you might want additional inputs for other sensors (temperature, door contact, etc.). You might also want outputs to control devices on site (fans, air conditioners, etc.).
Can the RTU generate alarms based on the sensor readings? Can it take corrective action, like turning on a fan or starting an air conditioner?
A local display can be very handy for monitoring readings, changing settings, etc. A keypad can be useful for making changes without having to connect to the device remotely.
Will the RTU be located in a space that is subject to extreme temperature, humidity, or other environmental conditions? If so, you'll want to make sure the RTU is rated for those conditions.
How will the RTU be powered? RTUs for telecom applications commonly run on -48 VDC or +24 VDC. Others can run on +12 VDC or even 110/220 VAC. Make sure the RTU you choose can be powered with what you have available for your application.
We manufacture quite a few different RTUs at DPS. All of them can be used for humidity monitoring. Which one you choose is entirely up to what else you'd like to monitor, how you'd like to monitor it, and what your site power voltage is. There are also specialized builds of each model that can survive a very wide temperature range when required.
As an example, the NetGuardian 832A can collect from 32 discrete sensors, 8 analog sensors (including multi-sensor weather stations), and can issue on-site commands with 8 control relay outputs.
The TempDefender is a smaller RTU with environmental monitoring of temperature and humidity as a primary focus. Its very name stems from its role as a temperature and humidity monitor.
Both of these RTUs mount in a standard 19" or 23" rack, but other options can wall-mount or DIN-rail-mount.
They also both communicate with the D-Wire temperature and humidity sensor(s).
There are a few different technologies used in humidity sensors that measure relative humidity, and each has its own advantages and disadvantages. The three most common technologies are: capacitive, resistive, and optical.
Advantages: Can be very accurate; often used in industrial and laboratory applications.
Disadvantages: More expensive than other technologies; can be sensitive to contamination.
Advantages: Inexpensive; fairly rugged; commonly used in HVAC applications.
Disadvantages: Not as accurate as other technologies; can be affected by contamination.
Advantages: No moving parts; can be very rugged; often used in outdoor applications.
Disadvantages: More expensive than other technologies; can be sensitive to dust and other particulates.
I hope this has been helpful in understanding the basics of humidity monitoring using detectors. If you have any further questions or would like to discuss your specific application, please give me a call. I'll be happy to help you choose the right solution for your needs.
Call me at 1-800-693-0351 or email me at email@example.com
Andrew Erickson is an Application Engineer at DPS Telecom, a manufacturer of semi-custom remote alarm monitoring systems based in Fresno, California. Andrew brings more than 16 years of experience building site monitoring solutions, developing intuitive user interfaces and documentation, and opt...
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