Tech Challenge 
Maintaining Environmental Conditions Sandy, a graduate student studying insect physiology, is in charge of keeping the walk-in incubator at the correct environmental conditions. The small room is not automated, so she has to monitor the different parameters and make adjustments to the control devices herself when necessary. For her research, she must have continuous, fairly accurate data on the various environmental conditions: 1°C for temperature and 3% or better on %RH. The day/night cycle is easy, because the lights are plugged into on/off timers. What should Sandy do about the temperature and humidity? A. Get a thermohygrometer such as the Oakton® Thermohygrometer with Digital Thermometer. B. Get a temperature and humidity paperless recorder, such as the Extech® Temperature/Humidity Paperless Recorder, and an optional alarm relay. C. Get a thermometer, such as the Cole-Parmer Thermometer with Time/Date Stamp and Wire Probe, and a psychrometer, such as a Pocket Sling Psychometer. D. Get a temperature and humidity chart recorder, such as the Temperature/Humidity Strip Chart Recorder. Answers: A. Get a thermohygrometer such as the Oakton® Thermohygrometer with Digital Thermometer. Incorrect. For this thermohygrometer, the accuracy of the humidity measurement is too low and Sandy would have to regularly log the temperature and humidity data, as well as make any adjustments to the environmental conditions. Sandy would have no way of knowing if the environmental conditions were out of acceptable limits because it has no alarm. B. Get a temperature and humidity paperless recorder, such as the Extech® Temperature/Humidity Paperless Recorder, and an optional alarm relay. Correct! This recorder measures temperature and humidity accurately, electronically records the data for download to a computer, and has an external alarm relay available. So, Sandy can work at her desk instead of having to stay near the incubator all day. C. Get a thermometer, such as the Cole-Parmer Thermometer with Time/Date Stamp and Wire Probe, and a psychrometer, such as a Pocket Sling Psychometer. Incorrect. This combination has good accuracy for humidity, but there is no data logging capability and no alarm. Sandy would have to check the devices regularly to log data and make adjustments to the conditions, and she would not know when the conditions were outside acceptable limits. D. Get a temperature and humidity chart recorder, such as the Temperature/Humidity Strip Chart Recorder.. Incorrect. Although the accuracy of the measurement is good and the instrument logs data, there is no alarm function to alert Sandy to unacceptable conditions. Plus, the record is on paper, which has to be typed into a spreadsheet by hand for data analysis. . Choosing a Vacuum Pump Vincent from No-Water Allowed, Inc. just purchased the Secador® Techni-dome® 360 Vacuum Desiccator and is looking for an appropriate vacuum pump to couple with it. The lab needs to achieve a vacuum level of at least 24" Hg, and live at sea level. What pump would you suggest they pair with the desiccator for their lab in the USA? B. A dry diaphragm vacuum pump? C. A PTFE-coated dry diaphragm vacuum pump? Answers: Correct! When sizing a vacuum pump you should multiply the total volume of the container being evacuated by 1.5 to determine the adequate free air capacity. Since this is a 65-L desiccator, we need a pump with a minimal free air capacity of 4.6 cfm (130 L/min). All other specifications, like maximum vacuum and power requirements, meet this user’s need at an economical price. B. A dry diaphragm vacuum pump? Incorrect. Although this unit is rated to reach a 29.8" Hg vacuum level, it does not have the free air capacity to adequately reach this vacuum level for such a large container. Plus, this pump would be much more than the user needs. C. A PTFE-coated dry diaphragm vacuum pump? Incorrect. This unit is unsuitable on many levels: the free air capacity is too low, it is powered by 12 volts DC, and it will not meet the vacuum level requirements of 24" Hg. Incorrect. When sizing a vacuum pump, multiply the total volume of the container being evacuated by 1.5 to determine the adequate free air capacity. Since this is a 65-L desiccator, we need a pump with a minimal free air capacity of 4.6 cfm (130 L/min). Although this pump meets this requirement and will reach the desired vacuum level, the price is overkill. |
