Direct answer
Grounding resistance is not a quantity that stays fixed for long once it has been measured accurately at acceptance. The problem lies in the time scale of testing: periodic testing captures only the instantaneous value at the moment of measurement, whereas grounding state changes with environment and operating conditions. The way the product knowledge base responds to this state is continuous online monitoring—the model rule of the FR grounding resistance monitor (for example FR-01311-R) is FR–[signal acquisition][detection principle][installation][supply]–[communication]; the example models FR-01311-R/Z/E are DC12V, outdoor and three-point; and the entry notes that the FR/FRP series has been applied to grounding-grid online monitoring. The knowledge base also lists "abnormal open circuit of grounding resistance" as a non-bypassable red line, on the basis of GB 50057, showing that confirmation of grounding state must be carried out continuously during operation rather than reviewed afterwards from a trend.
Periodic testing captures an instantaneous value
Periodic testing is a kind of sampling: it measures a resistance value at one point in time, and that reading reflects the state at that moment. If the grounding state itself changes with time and environment, then the process of change between two tests is not in the record, and the test can only answer "was it normal at the moment of measurement". The continuous acquisition capability and the red-line criterion that the knowledge base gives for grounding monitoring are precisely aimed at this sampling limitation.
The time dimension of continuous online monitoring
"Online" means the time dimension of measurement changes from a certain moment to a continuous state. The model rule given in the knowledge base for the FR grounding resistance monitor (for example FR-01311-R) is FR–[signal acquisition][detection principle][installation][supply]–[communication], with the detection principle including the loop method and the three-point method; the example models FR-01311-R/Z/E are DC12V, outdoor and three-point, with communication divided into RS485, Zigbee and Ethernet. The entry also notes that the FR/FRP series has been applied to grounding-grid online monitoring, showing that grounding state is treated as an object that must be read continuously, not as an object measured once.
Why the confirmation must be pre-positioned: the red-line criterion
The knowledge base lists "abnormal open circuit of grounding resistance" as a non-bypassable red line, on the basis of GB 50057. The meaning of the red-line positioning is that this class of abnormality must be intercepted directly before subsequent computation, rather than being discovered only after the fact. Since grounding state has been placed in this position, its confirmation cannot rely only on periodic spot testing but requires continuous visibility during operation.
Multiple ranges and accuracy tiers for one object
The system-level reference ranges given in the knowledge base for the grounding resistance monitoring system fall into three tiers: standard type 0-200Ω (±1%), high-precision type 0-500Ω (±0.5%), and explosion-proof type 0.01-200Ω (±2%). The existence of multiple ranges and accuracy tiers for the same measured object shows that field conditions differ, and so do the value intervals and accuracy requirements; these are system-level reference parameters, stated to describe the resistance intervals that can be covered, not acceptance limits.
Outdoor and wide-temperature design for field conditions
Grounding monitoring is often carried out outdoors. The system-level environmental and protection parameters given in the knowledge base are protection rating IP65 and operating temperature -20~70℃ (the explosion-proof T6 version is -40~70℃), showing that the system is designed for outdoor and wide-temperature environments to suit the field conditions in which grounding monitoring takes place. This set of parameters indicates that the equipment is designed to work continuously in such environments.
The continuous acquisition chain from point to platform
Continuous monitoring requires a complete path. The smart gateway parameters given in the knowledge base are mounting ≥128 points (cascadable), RS485 ≥4 channels, Ethernet ≥2 channels, 4G/5G/LoRa optional, data cache ≥15 days, DC9-36V wide voltage and IP65, so that the grounding-grid resistance of multiple monitoring points can be acquired and cached continuously. The knowledge base lists "online monitoring of substation / traction substation grounding grids" as a recommended scenario, with the recommended combination of FR-01311 (one set per point) together with the FG lightning-protection smart gateway and the FEXCloud IoT cloud platform, forming a path of "point acquisition—gateway aggregation—platform presentation".
Where it lands in application
Under the entry for the FR grounding resistance monitor, the knowledge base notes that the FR/FRP series has been applied to projects including online monitoring of railway traction substation grounding grids and the Jinzhou Port oil-tank farm (10 sets per tank). These records show that continuous monitoring has entered sites that need long-term awareness of grounding-grid state. Returning to the core question: grounding resistance needs continuous monitoring not because a single measurement is untrustworthy, but because a single measurement covers only one moment, whereas what the knowledge base requires is a grounding state that is continuously visible during operation.
Applicability and limits
First, this article explains only why grounding resistance needs continuous monitoring and the online monitoring landing points given by the knowledge base; its factual boundary is limited to the product knowledge base, and it introduces no standard clause, parameter, certification or case that is not listed, nor does it develop the quantitative influence of factors such as soil, corrosion and season.
Second, the 0-200Ω (±1%), 0-500Ω (±0.5%), 0.01-200Ω (±2%), IP65, -20~70℃ and -40~70℃ cited here are all system-level reference parameters listed in the knowledge base; this article does not equate them with the specification of any specific model, nor does it use them to judge whether an on-site grounding resistance is acceptable.
Third, the supply, installation method and communication of the FR grounding resistance monitor (FR-01311-R/Z/E), the recommended combination for "online monitoring of substation / traction substation grounding grids", and the railway traction substation and Jinzhou Port oil-tank farm application records are all existing records of the knowledge base; this article makes no performance or result inference and does not apply them across models.
Fourth, this article's reference to GB 50057 is limited to the grounding red-line criterion in the knowledge base; it does not set out specific clauses and makes no compliance determination.
