> For the complete documentation index, see [llms.txt](https://docs.bituo-technik.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.bituo-technik.com/faq/electrical-4.md). # Data & Measurement > Explain where the data displayed in the App comes from, how often it refreshes, and where it is stored. ### ⚡ Quick Answers
What accuracy standard do your meters follow? [SPM/SDM Products] Both SPM and SDM comply with [**IEC 61557-12**](https://webstore.iec.ch/publication/65510), the international standard specifically designed for **Power Metering and Monitoring Devices (PMDs)** — covering active power, reactive power, power factor, and energy measurement accuracy in a unified framework. This is distinct from IEC 62053, which applies to traditional utility billing meters. IEC 61557-12 is more appropriate for compact, embedded monitoring devices like SPM and SDM, and is increasingly adopted across the industry for this class of product. > 📖 For a deeper dive, the blog post "Understanding the IEC 61557-12 Standard That Makes Meter Comparisons Easier-[Part 1](https://blog.se.com/energy-management-energy-efficiency/energy-regulations/2016/10/18/understanding-iec-standard-makes-meter-comparisons-easier/) and [Part 2](https://blog.se.com/energy-management-energy-efficiency/energy-regulations/2016/10/27/understanding-iec-standard-makes-meter-comparisons-easier-part-2/)", written by [Mr Franck Gruffaz](https://blog.se.com/author/franck-gruffaz/), is a good introductory material for the standard and its applications.
Why does the SPM/SDM show lower (or different) energy consumption compared to another meter? Slight discrepancies are normal. If the difference is noticeable, it is typically due to one or more of the following: **1. CT Installation Issues (SDM Only)** Ensure each clamp CT is fully snapped shut with no debris in the core gap — even a small gap causes flux leakage and lower readings. **2. Calibration Accuracy vs. Consumer Smart Plugs** Consumer smart plugs are typically calibrated to a much looser tolerance than IEC Class 1, with errors more pronounced at low load levels. **3. Limited DC Component Tolerance (vs. Modern Utility Billing Meters)** SPM uses miniature CTs; SDM uses clamp CTs — both have limited immunity to DC components in the AC waveform. Modern utility billing meters are specifically rated for DC offset handling. High-power single-phase inverter-driven loads (e.g., heat pumps, variable-frequency drives) can produce asymmetric current waveforms that cause mild CT saturation, resulting in slightly lower readings. This is a known physical limitation of this class of monitors. **4. Low-Load / Standby Accuracy Range** If the monitored circuit runs mostly at very low standby power (average current below **Imin \~50mA**), readings may fall outside the specified accuracy range. A comparison in this range is not meaningful. **5. Accuracy Class Differences** SDM01 comply with Class 1 (IEC61557-12). Lower-class meters or smart pluggers (±2%\~±5%) will accumulate diverging errors over time, especially under reactive or mixed loads. **6. Other Causes** The above covers the most common scenarios, but measurement discrepancies can sometimes stem from factors specific to your installation or load profile. If you've worked through the above and the difference remains unexplained, we're happy to investigate together — and if it points to something we can improve in the product, we'll take it seriously. > 💡 **For a clean comparison:** Use a pure resistive load (e.g., 1000W heater) and compare **real-time Wattage**, not accumulated kWh.
How to download the historical data measured by SPM/SDM Meters (Tuya Version)? Previously, exporting historical energy data from standard Tuya connectivity products required complex cloud API configurations or third-party platforms like Home Assistant. To solve this, we have fully upgraded our Tuya connectivity product range—including both **Tuya Wi-Fi and Tuya Zigbee** versions—to the new **"Davidia" (Gongtong) firmware**. If you are using a Davidia-version SPM/SDM meter, you can download your data directly through the Smart Life App with zero programming required: * **One-Click Data Export:** Simply tap the download icon on the completely redesigned Historical Chart Page. Your historical bi-directional energy data will be sent directly to your email in a convenient spreadsheet format. * **Per-Phase Data Support:** For 3-phase models, you can even export historical data for each individual phase independently, which is perfect for precise analysis. > 📖 For a detailed UI guide and a full list of supported models featuring the data export function, please check out our [product update](https://shop.bituo-technik.com/blogs/tech-hub/product-update-energy-meters-using-tuya-wifi-module-now-support-bi-directional-data-export-email-delivery).
Tuya "Davidia" vs. "Basic" Version: What's the difference? Scheduled for **May 1, 2026**, all electricity meters produced and delivered by our company using Tuya AIoT services will be upgraded to the new **'Davidia'** version. The key differences between the Davidia version and the Basic version are as follows: **1. New Features** * **Data Export:** Added functionality to export historical energy data and send it directly via email in a convenient spreadsheet format (Excel/CSV). * **Per-Phase Data Support (3-Phase Models):** Users can now export and email historical data for each individual phase independently, allowing for more precise load monitoring and analysis. **2. Technical & UI Changes** * **Optimized Firmware:** The Davidia version utilizes specific, upgraded communication module firmware and PIDs from Tuya. * **User Interface:** The most noticeable difference for end-users is the App interface layout. The Davidia version features a redesigned Historical Chart Page and a brand-new Data Export Page. **UI Comparison** | Interface | Tuya "Davidia" Version | Tuya "Basic" Version | | ------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | **Historical Chart Page** |


| ![](https://68488808-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FTmsWivaZjkubbVKrCezC%2Fuploads%2FHPRHeGRhVFbgdLLVkd5e%2Fimage.png?alt=media\&token=2584a72c-8ba2-4885-aeed-4780ae4aa714) | | **Data Export Page** | ![](https://68488808-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FTmsWivaZjkubbVKrCezC%2Fuploads%2FLaeY39a9vghreNszVnwH%2Fimage.png?alt=media\&token=1dffbc2c-41e8-4ecd-9c44-c6d50b85898f) | **Not Available** | > 💡 **Note:** Some Davidia version units have already been sold prior to May 1, 2026. If you require the data export feature, please verify the firmware version with your vendor before purchase.
Does SPM/SDM support bi-directional energy measurement? [SPM/SDM Products] Yes! Both our SPM and SDM series support bi-directional energy measurement. They can accurately monitor both the energy consumed from the grid and the surplus energy exported back to the grid (e.g., from solar panels). Note: If your application requires high-speed local data transmission for real-time control—such as solar export limiting—we highly recommend choosing the SDM01 Combo Gen2 series, as its dedicated metering MCU can deliver stable power readings in under 150ms.
What accuracy standard does the SDM comply with? [SDM Products] The SDM series comply with **IEC 61557-12**, the international standard for Power Metering and Monitoring Devices (PMD). It is classified as **PMD-II / DD / Class 1**. * **PMD-II** means the device measures all core parameters: active power (P), reactive power (Q), apparent power (S), active energy (Ea), reactive energy (Er), frequency (f), current (I), voltage (U/V), and power factor (PF). * **DD** means the meter and its dedicated CT are calibrated and validated as a complete system. * **Class 1** means active power and energy are measured within ±1.0% under normal load conditions (≥ 4A at PF = 1). > This is different from IEC 62053-21, which only covers kWh billing accuracy. IEC 61557-12 covers all measured parameters in real time.
What is the difference between IEC 61557-12 and IEC 62053-21? [All Products] | | IEC 62053-21 | IEC 61557-12 | | ------------------------------------------- | ---------------------- | ------------------------------ | | Designed for | Utility billing meters | Power monitoring devices (PMD) | | Covers kWh | ✅ | ✅ | | Covers real-time P, Q, PF, I, V | ❌ | ✅ | | Suitable for export limiting / load control | ❌ | ✅ |
Does "Class 1" mean the the device is always accurate to ±1%? [All Products] IEC 61557-12 Class 1 does not guarantee ±1% accuracy under all conditions. The standard defines different uncertainty limits across different current ranges and power factor conditions — and this applies to every Class 1 PMD on the market, not just the SDM01. The table below reproduces the relevant portion of **IEC 61557-12:2021, Table 8** — the intrinsic uncertainty limits for active power and active energy, applicable to Class 1 (C = 1) PMD/DD devices: **Table 8 — Intrinsic Uncertainty Limits (Active Power & Energy, PMD/DD, C = 1)**
Current RangePower FactorUncertainty FormulaLimit at C = 1
5\%I_b \leq I < 10\%I_b11.0 \times C + 0.5±1.5%
10\%I_b \leq I \leq I_{max}11.0 \times C±1.0%
10\%I_b \leq I < 20\%I_b0.5L / 0.8C1.0 \times C + 0.5±1.5%
20\%I_b \leq I \leq I_{max}0.5L / 0.8C1.0 \times C±1.0%
*Note: For C ≥ 1, the standard sets no requirement below* $$5%I\_b$$ *at PF = 1, and below* $$10%I\_b$$ *at non-unity PF. This is consistent across all IEC 61557-12 Class 1 devices.* Example: Applied to the SDM01-TWM-12 ($$I\_b$$ = 20A, $$I\_{max}$$ = 120A) | Operating Zone | Current Range | Power Factor | Accuracy | | --------------------- | ------------- | ------------ | --------- | | Light load | 1A – 2A | 1 | **±1.5%** | | Normal load | 2A – 120A | 1 | **±1.0%** | | Light load, reactive | 2A – 4A | 0.5L / 0.8C | **±1.5%** | | Normal load, reactive | 4A – 120A | 0.5L / 0.8C | **±1.0%** | The ±1.0% zone covers the vast majority of real-world operating conditions. The ±1.5% tolerance only applies at very light loads — below 2A for this model — which represents a small fraction of typical operating time in any residential or commercial installation.
Can I use a third-party CT with the SDM? [SDM Products] No — and this is important for maintaining the accuracy specification. Under IEC 61557-12, accuracy is a **system property** of the meter + CT combination, not the meter alone. The CT's ratio error and phase displacement must be known and compensated in the meter's calibration. * **SDM01 Gen1:** Must use the factory-matched CT with the same Calibration ID. Substituting any other CT invalidates the Class 1 specification. * **SDM02:** Must use the factory-matched CT with the same Calibration ID. Substituting any other CT invalidates the Class 1 specification. * **SDM01 Gen2:** Compatible with any CT on the Bituo approved CT list. Each approved combination has been independently type-tested as a complete system. Using an unapproved CT may cause measurement errors that cannot be corrected by firmware.
What is the difference between SDM01 Gen1 and Gen2 in terms of accuracy? [SDM Products] Both generations meet **IEC 61557-12 Class 1** accuracy. The difference is in how that accuracy is achieved: | | Gen1 | Gen2 | | -------------- | -------------------------------------------- | --------------------------------------------- | | Accuracy class | Class 1 | Class 1 | | CT approach | Factory-matched pair (unique Calibration ID) | Approved CT list (multiple compatible models) | | CT flexibility | Fixed — must use matched CT | Flexible — choose from approved list | Gen1 is a tightly matched system ideal for fixed installations. Gen2 offers more flexibility for projects where CT aperture or current rating needs to vary.
What is a PMD, and how is it different from a regular energy meter? [All Products] A **Power Metering and Monitoring Device (PMD)**, as defined by IEC 61557-12, measures multiple electrical parameters simultaneously in real time — including active power, reactive power, apparent power, current, voltage, power factor, frequency, and bi-directional energy. A regular energy meter (e.g., a billing meter per IEC 62053-21) typically only accumulates kWh over time. It does not provide instantaneous power readings or reactive parameters. PMDs are used in applications where real-time power data is needed for control decisions — such as solar export limiting, EV charge management, and home energy automation.
### 🛠️ Detailed Guides * [How to Reset Tuya Smart Switches and Smart Meters](/faq/electrical-4/how-to-reset-tuya-smart-switches-and-smart-meters.md) `[SRS/SPM/SDM Products]`