Category Archives: TechNotes

What is Dew Point Temperature

Our state side colleagues have put together a great FAQ technical note explaining dew point temperature in more detail!

chilled mirror / dew point mirror
chilled mirror / dew point mirror

The FAQ technical note can be accessed here and answers the following key questions!

  1. What is dew point temperature?
  2. What is frost  point?
  3. When should I choose dew point as the parameter I measure?
  4. What are the pros and cons of measuring dew point versus relative humidity?
  5. Does dew point change as the ambient temperature changes?
  6. How does pressure affect dew point measurement?
  7. What are the common technologies for measuring dew point?
  8. Isn’t dew point temperature the same thing as wet bulb temperature?
  9. How do I know which technology is best for my application?
  10. Where can I buy a dew point instrument?

Rotronic produce precision low dew point sensors for low moisture applications in addition Rotronic UK is the UK distributor for world class MBW chilled mirrors, please contact us for additional information!

Dr Jeremy Wingate
Rotronic UK

Energy Efficiency and Reliability in Modern Data Centres

Introduction

Data centres are rapidly becoming the power houses of the modern world. Combined with the rise of digital industries, virtually all business operations now rely in some way on the transfer of data. As data transfer rates increase in tandem with an explosion in mobile communication the demands on data centre infra-structure are ever increasing.

It is estimated that by 2018 global data traffic will exceed 8500 exabytes (32% compound annual growth rate).

Data centres provide the infra-structure to support the transfer and hosting of data. They are often classified into 4 tiers. Tier 4 provides highest levels of redundancy, security and efficiency. For example, a Tier 4 data centre is required to have an uptime of 99.995% equivalent to less than 27 minutes downtime per year! Tier 4 sites have fully redundant systems, power supplies and biometric security. Zero downtime is the ideal as the costs incurred via end user penalties can be huge.

data centre tiers

Why the need to measure temperature, humidity and differential pressure?

Data centres must be maintained to specific environmental conditions to ensure the performance and longevity of the hardware installed. As standard, temperature must be 18-27 °C, dew point 5-15 °C dp and humidity no higher than 60 %rh. This ensures the hardware is at a suitable temperature, condensation is avoided and the chance of static build up is reduced (caused by low humidity).

A control range of ±9 °C may seem relatively broad, however 100% of the energy supplied to server hardware is converted to heat. In most data centres if the cooling system fails and servers are not shut down, heat levels will rise above a critical 35 °C within minutes or even seconds. If unchecked, temperature levels will rise causing hardware damage and can result in electrical fires.

Achieving the specified control range requires precision sensors and advanced control systems. Typically modern data centres are designed using computational fluid dynamics to ensure the very highest efficiency. Despite this it is estimated around 5% of US electrical energy used is for data centre cooling.

pue power usage effectiveness

Since 100% of electricity utilised by servers is converted to heat, theoretically a 100% efficient cooling system would require an equal amount of energy. Efficiency is measured by comparing total facility energy use, with IT equipment energy use. This is called Power Usage Effectiveness (PUE). Theoretically PUE can be 1 but typically reported values are above 2. By utilising precision measurements and design, modern data centres achieve PUEs of ~1.1!

An improvement of 0.5 in a data centre’s PUE  equates to a energy saving of ~£2.2 M & ~12,000 tonnes CO2 over 5 years (for a site with 1 MW load).

 

What solutions can Rotronic offer?

Rotronic provides a range of instruments for environmental monitoring and control. Reliable and precise outside air sensors and weather shields enable natural cooling to be utilised where possible.

Inside the data centres, Rotronic interchangeable HC2-S probes can provide a combination of precise, fast response temperature and humidity measurements with ease of calibration. Our latest PF4 differential pressure transmitters provide precision low drift measurements.

With both digital and a range of analogue outputs available as well as several probe mounting options, products can be selected for all applications.

Importantly though we aim to understand your needs and build a relationship with the goal of providing an appropriate solution, combining instruments, training, calibration and ongoing support.

Dr Jeremy WIngate
Rotronic UK

 

Technical Note 1 – Digital Integration of Rotronic devices

The Rotronic HygroClip2 was launched around four years ago and is used as standard with most of our devices. Underpinning the HygroClip2’s performance beyond the Rotronic sensor element is some impressive technology.

The Airchip3000 is the chip that provides high resolution measurement of the raw sensor outputs, temperature compensation and calibration correction tables which ultimately provides the high accuracy measurements our customers demand.  In addition, the Airchip provides digital and analogue communications. All the Rotronic instrumentation communicates digitally to these probes but these interface methods are possible without using a Rotronic handheld/logger/transmitter etc.

Lets explore what is possible…

Connections

Devices can be connected to your software or systems via USB, Ethernet, Serial or Wireless depending on the physical connections available. The AirChip itself has a simple RS232 output so additional hardware will be required for for anything but direct RS232 interface (to a Raspberry Pi GPIO for example).

Rotronic DLL

The Rotronic DLL provides a link between Rotronic devices and your software program (as well as our HW4 software). The DLL allows you to call up all functions within our devices that are accessible via our software. We have several example packages to make developing your own systems easier including;

– C++
– Visual Basic
– LabView
– Excel

The DLL can be integrated into wider software systems, if you have sufficient technical know-how. For example using using ctypes in Python allows the integration of Windows DLL. Python programs can then be used cross platform (Windows, Mac and Linux etc).

This approach is typically used when integrating our HC2 range of probes via our AC3001 Probe-USB converter cable. This way you can utilise our highest accuracy probes in a simple and efficient manor without any loss of accuracy due to digital-analogue conversions. It is also possible to quickly add the measured values into your existing projects. This is how our HygroGen2’s Autocal system communicates to the Rotronic probes during automated calibration and adjustment runs.

Example programs and DLL itself can be downloaded here

If you require support integrating our sensors into your systems please do not hesitate to contact us!

Direct Device Interface

In certain situations utilsing our DLL may not be appropriate for your project. So it is also possible to directly communicate with the Airchip3000 devices avoiding the DLL and using direct protocol commands. This is often a far simpler method and more commonly used when integrating to industrial systems.

With Ethernet and Serial devices communication if very easy using a terminal program (eg Putty) or direct from your Linux terminal (For USB some extra step are required explained at the end of this article).

1. Connecting to Rotronic devices via Putty (!!! USING USB? READ THE NOTE AT THE BOTTOM OF THIS POST !!!

Firstly, you simply need to connect to the relevant comm port or IP Address and send your commands. Serial interface settings are detailed below. For Ethernet simply use RAW connection and select port 2101 or use Telnet with Port 2001 (you will need your devices IP address)

Step 1 – Setup Serial Settings in Putty

Putty Setup

Step 2 – Force Echo On / Line Editing
I strongly recommend changing the Terminal settings to Force Echo (so you can see what you type and edit it)…

Putty Setting Echo

Step 3 – Connect
Now simply open your session…

Putty Open

All Airchip devices will respond to the command below, an example response is shown from a HC2-S probe.

Sent Command
{ 99rdd}

Return String
{F00rdd 001; 36.30;%rh;000;=; 24.30;°C;000;=;nc;—.- ;°C;000; ;001;V2.0-2;0061176056;HC2 ;000;C

Explaination ( “;” separated values)
{
F = Device Type
00 = RS485 address
rdd = command
001 = Device type

36.30 = value 1
%rh = value 1 units
000 = value 1 alarm condition
= = trend

24.30 = value 2
°C = value 2 units
000 = value 2 alarm condition
= = trend

nc = calculated value selected
—.- = calculated value
°C = calculated value units
000 = calculated value alarm condition
= calculated value trend

001 = hardware version
V2.0-2 = firmware version
0061176056 = serial number
HC2 = device name
000 = sensor alarm
C = checksum

Important Note! Using USB interface with Putty

By default all Rotronic USB interface cables will link to the Rotronic driver and try to use the DLL. However if you configure the cable to be a Virtual Comm Port you can use the simple serial connection method described above! So you can see every device  connection type can be interfaced using this method 🙂

To do this you need to force windows to use the standard FTDI driver and setup the Virtual Comm Port.

Step 1 Install FTDI Drives

Select the relevant drivers from this page for you OS http://www.ftdichip.com/Drivers/D2XX.htm

Step 2 – Force Windows to use new driver

Go to device manager (Control Panel, System, Device Manager)

1 – Click Update Driver
2 – Select Browse my computer for Driver
3 – Choose ‘Let my pick from a list’
4 – Click Have Disk
5 – Go to the FTDI folder and click  ftdibus.ini
6 – Select the USB Serial Port

Now you will see a new USB Serial Port in Device Manager under Ports (COMM AND LPT) – right click and select properties. Ensure the Port Settings are as below.

Baud rate : 19200
Data bits : 8
Parity : none
Stop bits : 1
Flow Control : none

You can now use the Virtual Comm Port in putty or other projects.

In my experience with bespoke software packages for a single device type the terminal connection is very simple.

For example a simple Python code to communicate with an Ethernet device is below…

try:
session = telnetlib.Telnet(192.168.1.1, 2001, 0.5)
except socket.timeout:
print (“socket timeout”)
else:
session.write(“{ 99RDD}”.encode(‘ascii’) + b”\r”)
output = session.read_until(b”/r/n/r/n#>”, timeout )
session.close()
print(output)

We will look at direct interface to the AirChip and available protocol options next time!

Comments or queries – let us know!!

Dr. Jeremy Wingate
Rotronic UK