Monitoring Temperature Sensors in Medical Refrigerators

The Wireless Temperature Monitoring (WTM) devices have arrived, now what do I do?

Okay, the long search for the optimal WTM system has been completed. The wireless technology works in all locations to be monitored. AC and/or battery powered devices are specified and arrive. Now what does one do? In this ongoing series about NYC Hospital Queens’ experience in selecting and installing a WTM system to monitor temperature-sensitive medications (e.g. vaccines) and blood in hospital refrigerators (Link to Article) some consideration as to the placement of temperature sensors in the hospital’s medical refrigerators is given.

Sure, the sensor will go into the refrigerator to monitor the storage temperature of prescriptions, vaccines, blood, or similar temperature-sensitive products. Once installed they will be turned on and begin collecting data. But what is actually sitting in the refrigerated space and what is the optimal placement inside the refrigerated space to ensure temperatures are being maintained properly? As in considering the issues so far discussed, wireless technology, electrical power source, etc., an understanding of what placing sensors in various locations will have on the temperature readings is needed.

First, what does the device look like? Was it planned that the temperature monitoring device sit wholly inside the refrigerator or just the sensor (temperature probe)? Some devices have integrated sensors and must sit inside the space to be monitored. Others use wired sensors where the sensor is placed into the wireless refrigerator sensor and WTM transmitter that sits outside the refrigerated space. Which configuration to use would have been determined during the testing phase. Let’s look at both options.

Installation Tips for Medical Refrigerator Sensors 

WTM devices that contain integrated sensors have the advantage of being able to be placed into a refrigerator. If they are battery powered there is no outside connection needed, so no need to have a wire going through a hole in the door gasket or refrigerator wall. However, if the devices are AC powered a power cord will need to pass from the inside of the refrigerator to the nearest electrical outlet, generally the same outlet used by the refrigerator (Note: Medical grade refrigerators and freezers often have wall penetrations/holes to introduce sensors, power cords).

Medical refrigerators that use wired sensors, meaning the sensor is at the end of an electrical cable like a phone or computer cable, are often placed outside the refrigerator. This helps with wireless connectivity because the wireless signal will not have to pass through the refrigerator’s signal robbing metal enclosure. The sensor is passed through a hole in the door gasket or wall and the other end is plugged into the appropriate slot in the WTM device.

This is a good thing because wires through gaskets generally compromise the refrigerator's door seal and let cold air escape and warm air enter. Wires through the walls have the same issue but leakage can be minimized with a gasket material around the penetration after the wire is in place.

Whether or not the entire WTM device or a wired sensor sits inside the refrigerator, proper placement of the sensor is important in order to maintain critical medication temperatures. SmartSense has published several pieces about temperature sensor placement in refrigerators. The most important lesson is that the middle of the middle shelf is likely the ideal place for the sensor. Door openings and the difference between the coolest air at the bottom of the compartment compared to the top of the compartment will be minimized with middle shelf locations. And placing away from the air outlets is also a good practice since cold air from the compressor can lead to lower temperature readings than would otherwise be seen. Additionally, an earlier piece in this series described the use of buffer vials that help prevent “false” alert messages when temperature spiked happen due to door opening and closing.

Set-Up Instructions for SmartSense by Digi Devices 

Everything is in place, plugged in, and ready to go - almost. The next pieces in this series will describe the process of setting up the user’s account and alert limits and the types of alerts one can receive. The series will wrap up with a piece that asks the question, “Okay, I have all this data at my disposal and I will be alerted when problems occur, now what?” Stay tuned or read more SmartSense by Digi technical support tips here.