Intro

Shipping and transporting precision instruments can be risky task, especially for the sensitive artifacts such as zener DC voltage standard Serious over packing and layers of foam isolation can help with reducing mechanical stresses and shocks to the fragile equipment but we can’t be 100% sure of good travels as accidents do happen. Zener standards are often required “hot” shipping under constant battery-backed power either with internal packs or with external UPS. This approach minimize possible hysteresis due to power cycling but does not help much with possible environment changes during transit.

First step to account for such possible shifts and induced calibration uncertainty error margins is to quantify environment parameters subjected to transported device. For this we would need a “black box” device that can record environment conditions at all times during transit and laboratory use of the artifact. Key requirements of such black box datalogger would be similar to list below.

• Compact size to facilitate easy placement in the shipping container with artifact standard
• Rugged construction that can survive possible shocks and handling during transit
• Integrated battery for power source during travel in a sealed container.
• No lithium battery that may require additional customs/transport company processing and cause delays in shipping
• Automatic periodical logging of key environment parameters, such as temperature, humidity, pressure with date/time stamps
• Support calibration functionality to ensure good quality of recorded data.
• Ability to download recorded data in easy manner, without obscure cloud subscription non-sense or proprietary formats.
• Preferably low cost so it could be included in every shipped artifact without much worry.

In this article we’ll look at few temperature-only dataloggers which can meet such feature list. I’ve recently acquired few VWR 6435 Memory-Loc and it’s brother with cute green elf bottles 6431 for testing. Big thanks to our friends at BPAI LLC from Baltimore, Maryland. Original manufacturer of these temperature data loggers is Control Company. But many brands customize these dataloggers with their badges and labels, so they can be found under many different brands. They sell in various configurations for prices in range 180 USD to 300 USD, depending on range and channel quantity. Traceable 6440, VWR International , LABRepCo and many others come as examples.

These loggers also can be acquired on secondary market for under 80 USD if you look patiently. Some models don’t have USB port for log storage and can be used only as bare temperature indicator, those sell for half the price new. Transcat has a catalog of the instruments made by Control Company here. Higher end models like 6500 even have Wi-Fi capability for remote notification of the temperatures or alarm events, so you could start panic even before package is delivered :).

Exterior look and use cases

Manual reveals quite a list of functions and modes that these little loggers have onboard.

Logger can store half a million samples with date code and timestamp, has alarm for high or low limits and ability to dump the data in CSV-format to USB stick. There is USB Type A host port on the side of the logger. It can also accept either two AAA batteries or AC power from the supplied power supply brick.

One or two sensors are included with the datalogger. They connect with 2-terminal 3.5mm jack. Here’s version with two “Bottle” sensors that physically average short-term temperature swings over longer time period.

Each datalogger is shipped with included ISO/IEC 17025 calibration report with claimed traceability to NIST. This is actually quite handy for important applications to confirm that datalogger shows correct temperatures at desired points.

For testing I’ve placed few of these dataloggers near equipment and in my TEC-based temperature chambers. Temperatures displayed matched expected values within ±0.1 °C which was a good sign. Agreement between different dataloggers and probes clamped together was also pretty close with similar ball-park deviation range.

Example location of 1000 Ω PT sensor near zener standards (zip tied to the metal shelf). Each PT1000 metal probe terminated with twisted pair of wires in chemically-resistant white PTFE insulation.

Diameter of the probe metal rod is 4.0 mm ± 0.05 mm. It might be bit too big to fit in some artifacts but fits in Tinsley 5685A or IET/Tegam/ESI SR104 with plenty room to spare. This enables datalogger for uses as temperature check source in laboratory environment as well, not just as shipping monitoring tool.

Datalogger fixed to the shelf with VELCRO® patch (supplied with dataloggers).

Dual channel “Bottle” Excursion-TRAC model was mounted on bench. One bottle was placed in mega-TEC chamber, while second is in mini-TEC chamber.

Chambers also had their dedicated 6440 dataloggers with one channel PT1000 sensors. Mega-TEC chamber:

It’s brother for mini-TEC as well:

Example data log CSV-file that was copied onto USB disk from one of the loggers provided below. Dumping data to USB stick is as simple as just plugging it in when datalogger is powered by AC adapter jack. Datalogger will not copy the memory dump to USB on battery power.

CSV-file with sample temperature log data

Logging interval can be configured with interval from 1 minute to 1 day. With fastest rate there is enough memory internally to store about a year of the datapoints. So these loggers can be used even for longer transits or general in-house laboratory monitoring in critical spots.

Teardown and quick analysis

Main microcontroller is Microchip PIC18F86K90 in the center of the board. It handles LCD refresh, data collection, calibration and configuration. Next to it we can find Linear Technologies LTC2493 which is nice four-channel input 24-bit Sigma-Delta ADC with current source and filtering, tailored for thermometry bridges and temperature measurements applications. It is interfaced to the MCU via I²C datalink, has external reference inputs and autocalibration block.

Wide SOIC-8 chip marked Winbond 25Q64JVSIQ is serial NOR FLASH memory chip for data storage. TAG-connect 6-pin footprint is available on the side of the board for firmware download and/or debugging. It’s probably standard SWD or JTAG pinout. LCD connects to mainboard via zebra strip rubber contactor.

Second 16-bit Microchip PIC24FJ64GB controller in TSSOP is designated for USB datalink handling and USB Host functionality for the USB Type A port. It’s quite interesting as this microcontroller does not seem to have hardware IP block for USB host, so perhaps developers implemented software host USB interface, which is messy but doable for slow USB 1.1 high-speed speeds. They would needed implementation of FAT filesystem support as well to write onto standard USB disks FS.

I’d also expect this auxiliary MCU to be power gated or power sourced directly from USB VBUS rail instead of the battery. Communication between main processor and USB controller probably done with serial interface like UART or SPI.

PCB is just 2 layers, so easy to figure out all the connections even visually.

Two calibration buttons imply the idea that calibration is done separately for each channel.

Experiment with shipping package internationally

Friend of mine needed a package with zener standards shipped from USA to Norway, during cold January winter between snow storms. Perfect test case for usefulness of such temperature datalogger, so one unit was donated for the case to explore the temperature changes during this international journey.

Package was shipped out via DHL international service on January 27, 2025 at 13:38 (GMT-5). Outside temperature on that day was +4 °C. Temperature logger was placed inside of the plastic hard-case with two Wavetek/Fluke 7000 reference cells and whole thing was double boxed with padding materials. Package was delivered at the destination in Norway on January 29, 2025 at 14:56 and later opened by owner at 18:30 (GMT+1). Air temperature outside was reported at -2 °C. Total transit duration was 46 hours (2812 minutes).

CSV-file was downloaded from logger

With help of small Python script and matplotlib we can generate a chart.

Python script to generate plot from CSV-datafile

Running script results in below output:

Minimum recorded temperature inside of the plastic case equals +10.03 °C and maximum at +32.06 °C, when box was closed up and sealed in the box. There is no “turn off” switch in Wavetek/Fluke 7000 reference cells, so they ran hot until internal batteries were depleted, which usually takes about 10-15 hours, depending on state of the batteries and temperature. During shipping two low temperature spots were observed, at about noon next day January 28 and early in the morning on January 29, prior to delivery. Most likely these are time periods when package was on the truck for transfers/delivery.

Overall temperature changes were rather smooth and at no point references were subjected to freezing cold temperatures, which is unwanted for sensitive 7-digit capable LTZ1000A-based cells. Obviously additional channels like humidity, pressure and acceleration would be most welcome addition for such sensitive packages shipments, but I’d argue that having temperature logging already much better than having no logging at all and hoping for “it will be alright, I promise” situation.

Summary

Overall these are very handy and every serious metrology tech should have at least one of these to bundle together with precision standards during shipping/transit from/to calibration laboratory to have confidence of environment stress effects on the artifact standards.

If enough interest generated from this post, I might do separate tests of PT1000 sensors that come with these dataloggers, with idea of reusing them with another recorders, such as Fluke 1529 Chub-E4. If you are interested and want to discuss details, you are welcome at our own IRC chat server: xdevs.com (port 6010, channel: #xDevs.com) or by reaching out to us with email.