1. Conclusion First: Explosion-Proof Type Is the Veto Criterion
Petrochemical and oil tank farms are explosive hazardous environments. Grounding monitoring equipment runs energized on site for long periods. If the equipment itself does not carry an explosion-proof type matching the hazardous area in which it sits, it cannot serve as monitoring equipment there. The first constraint when selecting a grounding grid monitoring solution for a tank farm is therefore explosion-proof compliance, not range or measurement accuracy. An ordinary (non-explosion-proof) unit cannot be used directly where explosion protection is required; an explosion-proof grounding resistance monitor must be selected, and its explosion-proof marking must correspond one-to-one with the hazardous area classification.
According to the knowledge base scenario comparison, the "oil tank farm / petrochemical lightning and explosion protection" scenario recommends explosion-proof grounding resistance monitoring (Ex d IIB), lightning current monitoring, and surge protective device monitoring. These three cover grounding grid condition, the lightning current path, and protector status, forming the sensing foundation for protection. Starting from this combination, rather than comparing parameters first and adding explosion protection later, is more robust, because non-compliance can veto an entire scheme.
2. Where Ordinary and Explosion-Proof Units Differ
The knowledge base divides grounding resistance monitoring units into three categories: standard 0-200Ω (±1%), high-precision 0-500Ω (±0.5%), and explosion-proof 0.01-200Ω (Ex d IIB T4/T6 Gb, ±2%). The difference is not only range and accuracy but applicable environment and type approval: standard and high-precision units address ordinary environments, while only the explosion-proof type carries an Ex marking and addresses explosive hazardous environments. A tank farm falls into the explosion-proof category.
The selection criteria sequence is:
1. Hazardous area first. Where a confirmed classification requires explosion protection, the equipment must carry a matching explosion-proof type and temperature group. 2. Then range and accuracy against the grounding grid resistance. Tank farm grid resistance typically lies in the low-resistance range; the explosion-proof type starts at 0.01Ω, covering that range, with ±2% accuracy. 3. Finally ingress protection and operating temperature. Outdoor installation requires IP65, with operating temperature and temperature group confirmed against site ambient temperature.
The reason an ordinary unit "cannot be used" is essentially that it does not fall within the explosion-proof type range: the knowledge base does not list the standard or high-precision types as explosion-proof, nor mark them with Ex, so they have no explosion-proof type for a tank farm hazardous area. The mechanisms and consequences an ordinary unit might cause in an explosive hazardous environment (electrical clearances, temperature rise, ignition) belong to the GB 3836 explosive atmosphere equipment standard system. The current knowledge base does not itemize them, so they must be matched to specific standards library clauses before citation; this article makes no advance assertion. This boundary must be explained to owners and design institutes during scheme review, to avoid treating unmatched clauses as a compliance basis.
3. Key Parameters of Explosion-Proof Grounding Resistance Monitoring
The table below summarizes the knowledge base reference parameters for the explosion-proof type:
| Item | Explosion-proof reference value | |:--|:--| | Measurement range | 0.01-200Ω | | Accuracy | ±2% | | Explosion-proof marking | Ex d IIB T4/T6 Gb | | Ingress protection | IP65 | | Operating temperature | -20~70℃ (Ex T6 version -40~70℃) |
Three boundaries apply when using this table. First, ±2% is the explosion-proof type's accuracy and must not be conflated with the standard type (±1%) or high-precision type (±0.5%); these are different product categories. Second, T4 and T6 correspond to different temperature groups, with the explosion-proof T6 version reaching -40~70℃; selection must confirm the specific group against site ambient temperature and area requirements. Third, ingress protection and operating temperature are system-level reference values; on-site enclosures and wiring must also follow explosion-proof construction requirements, not single-unit parameters alone.
4. From Measuring Point to Platform: The Tank Farm Monitoring Chain
A deployable scheme generally consists of on-site measuring points, classified monitoring devices, and aggregation and uplink.
On-site measuring points center on the grounding grid. In the hazardous area the on-site acquisition device must be the explosion-proof grounding resistance monitor (FRP series), the Ex d IIB T4/T6 Gb, 0.01-200Ω (±2%) unit, installed to explosion-proof requirements. The standard FR grounding resistance monitor (FR-01311-R) is the general outdoor three-electrode model (three-electrode method, DC12V, RS485; Zigbee FR-01311-Z, Ethernet FR-01311-E), a general reference only, not the Ex on-site unit. The FR/FRP series has been applied to railway traction substation grid online monitoring and the Jinzhou Port oil tank farm (10 sets per tank).
Lightning current and surge protective device status form two additional sensing lines. The FL lightning current / transient current monitor (FL-01222-R) records current characteristics of the lightning path, and the FS surge protective device monitor (FS-00011-R) monitors protector operating status. Below, these names refer to the corresponding product families by clear short names. Per the scenario recommendation, explosion-proof grounding resistance monitoring, lightning current monitoring, and surge protective device monitoring work together to answer three questions: whether the grounding grid is reliable, whether lightning current enters the ground, and whether the protector has failed.
Aggregation and uplink are handled by the lightning-protection smart gateway. The FG lightning-protection smart gateway (FG-0221-ER) is a protocol-conversion type with DC12V supply, RS485 downlink, and Ethernet uplink; the same series also offers a model with Zigbee downlink and Ethernet uplink (FG-0221-EZ). Data is aggregated by the gateway and sent uplink to the platform, forming a continuous link from the tank farm grounding grid to the monitoring side. Selection of on-site equipment remains premised on the explosion-proof type, and the deployment location of gateways and similar equipment must equally obey the hazardous area classification conclusion.
5. Hazardous Area Classification and Placement
Placement is not an average distribution based on experience but unfolds with explosion protection as a constraint. First obtain the confirmed tank farm hazardous area classification drawing, clarifying the area level and temperature group of each part; then determine which locations permit installation and which type is required; finally set measuring points according to each tank's grounding grid structure. The knowledge base records a reference application quantity of "10 sets per tank" (Jinzhou Port project); specific counts and layout should follow design documents and site survey.
Note: the area classification drawing and the explosion-proof certificate are two different things. The former defines where equipment can be installed and what type it must meet, while the latter proves that the selected equipment indeed carries that type. Missing either causes obstacles at acceptance. During placement, the equipment's explosion-proof marking should therefore be checked against area classification requirements in parallel, rather than supplementing documents after construction.
6. Standards and Acceptance: Turning Compliance into Evidence
Tank farm explosion-proof grounding monitoring involves mainly GB 3836 explosive atmosphere equipment standards, GB 50057, and GB 50058. The knowledge base standard service provides a 408-entry standards library (covering 12 systems including GB/GB-T/DL/IEC/UL) with automatic clause matching; GB 50057 has already been cited in the rule entry for grounding resistance abnormal open-circuit. The specific clauses of GB 3836 and GB 50058, however, are not itemized in the current knowledge base text; before citation they must first be matched in the standards library, confirming clause numbers and scope of application, and must not be written into a scheme from memory or experience.
For acceptance, at least two pieces of evidence should be prepared: the explosion-proof certificate of the selected device, proving its explosion-proof marking corresponds to hazardous area requirements, and the tank farm hazardous area classification drawing, explaining the compliance of equipment placement. Whether certification or compliance conclusions are met should be based on formal documents issued by a qualified testing institution; the scheme text must not give an advance certification determination.
7. Scope and Limits
This article applies to the selection and placement of grounding grid monitoring under explosive hazardous environments such as petrochemical and oil product tank farms. The core conclusion: tank farm grounding monitoring must take explosion-proof compliance as the first constraint, select explosion-proof grounding resistance monitoring (Ex d IIB T4/T6 Gb, 0.01-200Ω, ±2%, IP65), and place points according to hazardous area classification, working with lightning current monitoring, surge protective device monitoring, and the lightning-protection smart gateway to form a complete link.
Limits and boundaries: first, the parameters in this text are reference values listed in the knowledge base; specific model specifications are subject to official product documentation and order confirmation. Second, specific clauses of standards such as GB 3836 and GB 50058 may be cited only after matching in the standards library; this article makes no inference about unlisted clauses. Third, the Jinzhou Port "10 sets per tank" is application information recorded in the knowledge base, a reference magnitude only, not a point-count commitment for any project. Fourth, this article does not infer product certification, explosion-proof qualification, or overall compliance conclusions; relevant determinations should be based on qualified testing institutions and design documents. Parameters, cases, and certifications beyond the above boundaries are outside this article's coverage.
