DGA-500 — Standalone Dissolved Hydrogen Sensor for Transformers
A dissolved-hydrogen sensor that mounts independently on the transformer body, installed directly at the transformer ball valve and suitable for outdoor service. IP67 protection together with an applicable oil temperature of −40 ~ 105 ℃ allows long-term operation in outdoor transformer environments. The chip uses a palladium alloy thin-film resistor structure with a mature, stable Pd-alloy doping system, giving excellent long-term stability and freedom from periodic maintenance. In addition to dissolved hydrogen and oil temperature, the DGA-500 can be supplied with an optional moisture sensor and an optional oil pressure sensor.
Mounts directly at the transformer ball valve — IP67, −40 ~ 105 ℃ applicable oil temperature
Key Features
Solid-State Palladium Alloy Thin-Film
The chip uses a palladium alloy thin-film resistor structure with a mature, stable Pd-alloy doping system and specific composite thin-film fabrication, giving excellent long-term stability and sensitivity with no oil-gas separation.
Hydrogen-Specific Coating
A specific coating lets the sensor work reliably in backgrounds containing CO and CH compounds, so detection accuracy is not affected by other gases.
Hydrogen Detection in Different Backgrounds
Supports on-line hydrogen monitoring in mixed-gas backgrounds such as N₂, pure O₂ and inert gases.
Self-Regulating Working Temperature
A thin-film temperature sensor is integrated on the chip, allowing the working temperature to be adjusted automatically — no external temperature or flow-control devices are required.
Optional Moisture and Oil Pressure
Add a moisture sensor (0 ~ 100 %RS) and an oil pressure sensor (0 ~ 1 MPa) to the dissolved hydrogen and oil temperature measurement.
IP67, Outdoor Capable
IP67 protection with a −40 ~ 105 ℃ applicable oil temperature for long-term outdoor service. A corrosion-proof enclosure is available as an option for harsher site conditions.
Digital and 4 ~ 20 mA Analog Outputs
RS-485 with Modbus_RTU for configuration and data, plus an isolated 4 ~ 20 mA analog output whose span is configurable to the reporting range — so the DGA-500 can drive a SCADA or PLC analog input directly.
Technical Specifications
Dissolved Hydrogen
| Detection Principle | Palladium alloy thin film |
| Measuring Range | 5 ~ 5000 ppm |
| Limit of Detection | 5 ppm |
| Accuracy | ±15% reading or ±5 ppm (whichever is greater) |
| Repeatability | ±5% reading or ±5 ppm (whichever is greater) |
| Resolution | 1 ppm |
| Applicable Oil Temperature | −40 ~ 105 ℃ |
| Response Time τ90 | < 30 min (oil concentration above 100 ppm) |
Moisture (optional)
| Measuring Range | 0 ~ 100 %RS |
| Accuracy at 20 ℃ | 0 ~ 90 %RS: ±2 %RS 90 ~ 100 %RS: ±3 %RS |
| Response Time τ90 | < 10 min |
Oil Temperature
| Measuring Range | −40 ~ 120 ℃ |
| Accuracy at 20 ℃ | ±1 ℃ |
Oil Pressure (optional)
| Measuring Range | 0 ~ 1 MPa |
| Accuracy | ±1 % F.S. |
| Resolution | 0.1 kPa |
| Overload Capacity | 3 MPa |
Electrical & Other
| Power Supply | 24 V DC ±10%, 0.3 A (max) |
| Digital Output | RS-485 |
| Communication Protocol | Modbus_RTU |
| Analog Output | Isolated 4 ~ 20 mA, span configurable (fault 3.5 mA, not-ready 2.0 mA) |
| Ingress Protection | IP67 |
| Data Storage | Default interval 30 s (adjustable), 74,604 entries |
| Expected Life | 10 years |
| Weight | ≤ 500 g |
Type Configurations
| DGA-500 Base | Dissolved hydrogen and oil temperature sensor |
| DGA-500 with moisture | Plus moisture sensor |
| DGA-500 with moisture and oil pressure | Plus moisture and oil pressure sensors |
| Corrosion-proof enclosure | Optional, for DGA-500 |
Outline Dimensions
| Body Length | 226 mm |
| Probe Rod Length | 110 mm |
| Overall Length | 241.5 mm |
| Probe Rod Diameter | φ12.7 mm |
| Probe Root to Fitting | ≤ 45 mm |
| Process Connection | 1/2 in. two-ferrule tube fittings |
Range Limit
Range limit: the DGA-500 may only be used for hydrogen measurement in oil below 5000 ppm. Exceeding this range may cause the sensor chip to drift or even fail. Operation beyond the measuring range may cause irreversible damage to the sensor probe. A corrosion-proof enclosure is available as an option for this product.
Calibration follows the product manual: save the current state with the DA command, take an oil sample near the probe for off-line DGA analysis per ASTM D3612, and if the deviation exceeds 15% calibrate to the actual value with the DB command. The DX command clears the calibration data and returns the unit to factory calibration. Oil temperature, pressure and moisture calibration is performed with the CT command over RS-232 or via the MODBUS_RTU protocol.
Model Comparison
| Feature | DGA-300 (OEM) | DGA-500 (Standalone) | DGA-200 (Integrated) | DGA-900 (Multi-Gas) |
|---|---|---|---|---|
| H₂ Range | 2 ~ 2000 ppm | 5 ~ 5000 ppm | 5 ~ 5000 ppm | — |
| H₂ Detection Limit | 2 ppm | 5 ppm | Not specified | — |
| H₂ Accuracy | ±20% or ±2 ppm | ±15% or ±5 ppm | ±15% or ±5 ppm | — |
| Applicable Oil Temperature | 0 ~ 60 ℃ | −40 ~ 105 ℃ | −40 ~ 105 ℃ | — |
| Multi-Gas | — | — | — | 9 gases + moisture |
| Sensor Technology | Pd alloy MOSFET thin film | Pd alloy thin-film resistor | Palladium alloy thin film | Pd Thin-Film + LPAS |
| MODBUS | ✓ | ✓ | ✓ | ✓ |
| IEC 61850 | — | — | — | ✓ |
| Rating | IP67 | IP67 | IP66 | — |
| Weight | ≤ 350 g | ≤ 500 g | approx. 1.75 kg | — |
| Best For | OEM Integration | Standalone Transformer Mounting | Distribution Transformer Fleets | Critical Asset Protection |
The DGA-900 column repeats the figures already published on the DGA-900 product page and was not revised here; “—” marks a row not compared on this page. See the DGA-900 product page for its full specification.
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