Data logger

01

Size sample interval, memory and run time

The US National Park Service, comparing temperature and humidity loggers, notes that memory is quoted either as paired readings or as total individual readings, so divide by the number of active channels to compare; enabling more channels gives fewer sets of readings. Battery life depends on battery type and sampling rate, display and alarm features use power, and for trend monitoring it suggests enough battery for a full year. [1]

Renke's WiFi temperature and humidity logger, for example, stores 65,000 groups with a recording interval set from 1 minute to 1 hour. [2]

Editorial calculation: at 1-minute intervals, 65,000 records last 65,000 minutes, about 45 days; at the 15-minute interval NPS used for comparison, they last 975,000 minutes, about 677 days or 1.9 years. [2] [1] Check that battery life, not just memory, covers the same period.

Give the supplier the signals, channel count, interval, run time between downloads, power source, environment, accuracy and calibration needs, alarms and how data must be retrieved or uploaded.

02

Check inputs, accuracy, isolation and calibration

NPS notes that accuracy depends on sensor type, quality and calibration and can vary across the range; a one-point calibration checks mid-range only, while two or more points cover more of the range; NPS writes that “Manufacturer recommended recalibration times range from 6 months to 3 years, with most advocating annual calibration”. [1]

Renke states ±0.5 °C and ±3% RH accuracy at 25 °C and 60% RH, 0.1 °C and 0.1% RH resolution, and long-term drift of 0.1 °C and 1% RH per year or less. [2] Accuracy and resolution are different numbers; compare both.

For multi-channel test logging, Chroma's 51101 series lists 8- and 64-channel models, eight thermocouple types, per-channel cold-junction compensation, voltage adaptors to ±10 V and ±480 V DC, 1,000 V DC channel-to-channel isolation and up to 5 samples per second per channel; Chroma notes that multiplexed loggers slow per channel as channels are added, while its design does not. [3]

Editorial calculation: 64 channels × 5 samples/s = 320 samples/s, or 27,648,000 samples per day; check storage, PC software and file handling for that volume. [3]

03

Compare what suppliers offer

Suppliers linked to this page list temperature and humidity loggers, multi-channel and signal loggers, and remote monitoring loggers. [2] [3]

Renke lists WiFi and Ethernet temperature and humidity loggers; Hairuis lists USB, GSM and WiFi temperature and humidity loggers, thermocouple, PT100, 4–20 mA and 0–30 V loggers; HLY lists single-use and reusable cold-chain loggers and 4G trackers; Rika and Tsingsense list loggers for weather stations; GINTEC lists DCT20S and C2000 loggers for structural monitoring; ICP DAS lists eLogger software and EZ Data Logger devices; Vhandy lists CAN-bus data recorders; Lonnmeter lists data loggers among measuring instruments; Chroma lists thermal and multi-function loggers. [2] [3]

04

Write minimum logger specs for a regulated cold store

Guidelines from the US National Institute of Standards and Technology (NIST), funded by the Centers for Disease Control and Prevention, set minimum data logger features for a vaccine refrigerator held at 2 °C to 8 °C: a detachable probe kept in a liquid-filled bottle (cable over 1 m preferred); at least one reading per 15 minutes; memory for 4,000 readings, about 39 days at that rate, with recording stopping when full; −20 °C to 40 °C operating range; ±0.5 °C uncertainty (accuracy) from −1 °C to 15 °C; ±0.1 °C resolution; and at least 6 months of battery life. [4]

It also asks for a display with a high/low alarm indicator, user-adjustable alarms set at 2 °C and 8 °C, and software that downloads over a port such as USB, graphs the data, shows total time outside the limits and exports csv, Excel or txt files. Download at least weekly and at once after any alarm. [4]

Editorial calculation: a week at one reading per 15 minutes is 672 readings (7 × 24 × 4), 16.8% of the 4,000-reading minimum; 4,000 × 15 minutes = 60,000 minutes, 41.7 days, against NIST's stated figure of about 39 days. [4]

05

Trace the logger components

This is a functional reference built from the sources cited; it is not one maker's parts list.

06

Fill the specification fields with values for your application

A data logger quotation needs values for your signals and use. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the signals, schedule and data needs together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Signals: [temperature, humidity, thermocouple, voltage, current, bus; ranges]
Channels: [number; isolation between channels]
Schedule: [interval; run time; start and stop]
Accuracy: [per signal; calibration points; certificate]
Power: [battery, USB or external; battery life at interval]
Data: [memory; download or upload; software; alarms]
Environment: [temperature; humidity; IP rating]

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