How Do Manual and Automatic Monitoring Differ?
Manual and automatic monitoring differ in who takes the readings and how often. Both mostly use the same instruments and answer the same engineering question: how far has the ground or structure moved so far? In manual monitoring, staff carry a readout unit or a level instrument to each measuring point at the frequency specified in the project specification, record the values and bring them back to process into graphs. In automatic monitoring, the sensors stay wired to a datalogger on site, which takes readings on its own at preset times 24 hours a day and sends the data to a server over a cellular network or WiFi.
The most common misconception is that an automatic system gives more accurate readings. In fact, accuracy comes from the sensor itself and how it is installed, not from the system reading itself. The same sensor read with a handheld readout or a datalogger gives readings of similar resolution. Where an automatic system is clearly superior is resolution along the time axis: hourly or minute-by-minute data reveal short-term trends, the effect of each construction activity, and changes at night or on holidays that periodic manual readings cannot capture.
Conversely, manual reading offers something an automatic system cannot: an engineer's eyes on site. Every time staff go in to take readings, they see new cracks, seepage, soil loss behind the retaining wall, loose struts and the condition of the sensors themselves. This observational information is often worth more than the numbers. For an overview of every instrument type and what each one does, see the geotechnical instrumentation guide
The 3D view below places the two kinds of site side by side. On the left, staff walk from point to point taking readings; on the right, sensors are wired into a datalogger that sends data to the cloud. Pay particular attention to the graph in the lower panel: the value jumps between rounds 3 and 4. The automatic system sees it and issues an alert at that time, whereas manual reading only finds out at round 4.
Which Instruments Can Be Read Automatically and Which Need People?
Instruments that output an electrical signal can be read automatically, while instruments that require surveying or a manually lowered probe still need people to read them. If a sensor outputs an electrical signal that can be connected to a datalogger, it can be automated straight away. This table summarizes the instruments in both groups.
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| Equipment | Measures | Reading method | Automatable |
|---|---|---|---|
| Vibrating Wire Piezometer | Pore water pressure | Electrical signal to datalogger | Yes |
| Strain Gauge | Strain in reinforcement or struts | Electrical signal to datalogger | Yes |
| Tiltmeter | Tilt of buildings and retaining walls | Electrical signal to datalogger | Yes |
| In-place Inclinometer | Lateral movement | A string of sensors left in the casing, wired to a datalogger | Yes |
| Traversing inclinometer (Probe-type) | Lateral movement | Staff lower the probe depth interval by depth interval | Manual |
| Standpipe Piezometer / Observation Well | Water level in pipe | Water level meter lowered into pipe | Manual |
| Settlement Plate / Surface Settlement Marker / Multi-level Settlement Point | Settlement | Level survey | Manual |
The automatable group comprises 4 types: the vibrating wire piezometer, which measures pore water pressure directly and is the instrument most often automated; the strain gauge, which measures strain in reinforcement or struts; the tiltmeter, which measures the tilt of buildings and retaining walls; and the in-place inclinometer, which uses a string of sensors left in the inclinometer casing for the whole project instead of lowering a probe each time.
The group that still needs people includes settlement plates, surface settlement markers and multi-level settlement points, which are read by level surveying; standpipe piezometers and observation wells, read with a water level meter lowered into the pipe; and probe-type inclinometers following ASTM D6230, which require staff to lower the probe interval by interval on both the down and up passes. For more on these two groups, see Piezometers: measuring pore water pressure and Inclinometers: measuring lateral movement
Many projects decide to go automatic only after the instruments have been installed, which is often too late, because the choice of sensor type at the outset determines whether it can be connected to an automatic system. For example, if standpipe piezometers have already been installed but continuous data are needed later, new vibrating wire piezometers have to be drilled and installed. This decision should be made together with the layout of measuring points.
What Does an Automatic Monitoring System Consist Of?
An automatic monitoring system is a chain of 4 linked data components: the sensors on site, the datalogger, data transmission, and the cloud platform with alerts. If any one of them fails, the data stop immediately. There must also be a fifth component: site visits by staff to maintain the system and check actual conditions. System design must therefore consider the robustness of every component, not just selecting good sensors.
Often overlooked are power and protection. Most field systems run on batteries with solar panels. If the panel and battery are undersized for the rainy season, when sunshine is limited, the system shuts down intermittently and data are lost exactly when they are needed most. The other issue is lightning and surge protection along signal cables tens of meters long, which is the most frequent cause of datalogger and sensor damage on Thai sites.
Another issue is temperature compensation. Vibrating wire sensors and strain gauges also respond to temperature, so the system must record temperature alongside the measured values and apply the correction given by the manufacturer on each sensor's calibration certificate. Otherwise, readings will rise and fall in a daily cycle with air temperature and be mistaken for structural movement. For vibrating wire pore pressure sensors there is also guidance on acceptance testing before installation in ASTM D7764, which helps weed out faulty sensors before they go into the borehole.
How Do Manual and Automatic Monitoring Compare on Each Aspect?
Manual monitoring has a lower upfront cost and works with every instrument type, while automatic monitoring provides continuous data and issues alerts on its own but only works with sensors that output an electrical signal. The table below summarizes the differences that drive real project decisions, assuming the same sensor type is used in both cases.
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| Topic | Manual Monitoring | Automatic (Real-time) Monitoring |
|---|---|---|
| Reading method | Staff visit the site and read with a handheld readout or level instrument | Datalogger reads automatically at preset times |
| Data frequency | Discrete points at each site visit | Continuous 24 hours a day; adjustable from every 1 minute to daily |
| Speed of detecting abnormal readings | Known at the next reading round | Automatic alert at the preset transmission interval |
| Accuracy of readings | Similar, because it depends on the sensor type and installation, not on who reads it | |
| Applicable instruments | All types, including level surveying | Only sensors that output an electrical signal |
| Upfront cost | Lower | Higher, due to the datalogger, power system and cabling |
| Cost of more frequent readings | Increases with the number of reading visits | Almost no increase |
| Seeing actual site conditions | Yes cracks, seepage, abnormal struts | No sees only sensor readings |
| Risk of data gaps | Gaps when the site cannot be accessed, e.g. rain or restricted areas | Gaps when power runs out, the signal fails or cables are damaged |
| Best for | Long-term earth fills, slowly changing behavior, limited budgets | Urban deep excavations, work near adjacent buildings, work needing immediate warning |
The takeaway from the table is that the two approaches do not compete on data quality but on acceptable risk. If the damage from a problem would be high and behavior changes quickly, finding out a week late can cost more than the entire automatic system. The clearest example of work that meets this condition is deep excavation in urban areas, explained in Deep excavation monitoring in Bangkok soft clay
How Does an Automatic Alert System Work?
An automatic alert system compares each reading with preset thresholds and sends a message to the responsible people when a reading exceeds a threshold. This, more than the graphs on screen, is the heart of a real-time system. International practice sets thresholds in stages, typically 3 levels.
- Alert level: readings start trending the wrong way; increase monitoring frequency
- Action level: review work methods and prepare remedial measures
- Alarm level (stop work): stop the activity causing it and carry out remedial work immediately
The values for each level have no universal standard. They must be set by the design engineer from the analysis of that particular project, e.g. the design movement values, the distance to adjacent buildings and the sensitivity of surrounding structures. Copying threshold values from another project is a direct risk.
The most common problem with alert systems is false alarms. A one-off spike from signal noise, a rapid temperature change or a battery voltage drop makes the system send messages even though the structure is fine. When this happens often, everyone stops paying attention to alerts. The remedy is to require several consecutive exceedances before an alert is sent, route alerts to different recipients by severity, and assign someone to check every alert, with the final conclusion always coming from an engineer, not from the system.
Which Should You Choose? 5 Decision Criteria
Choose by asking one question: "How much damage would finding out a week late cause?", not "Which one is better?" The following 5 criteria can support the decision.
1. Consequences if a problem occurs. Deep excavations next to old buildings, work near underground utilities, or work with people working beneath the at-risk zone should use an automatic system, because the time to detection directly affects safety.
2. Rate of the behavior being monitored. Settlement of earth fill on soft clay changes over weeks to months, so periodic manual reading is sufficient. This is unlike the movement of a retaining wall during excavation, which can change within a single day.
3. Instrument types specified in the design. If the monitoring plan relies mainly on settlement plates and level surveying, an automatic system adds little. But if vibrating wire piezometers or strain gauges are already specified, connecting them to a datalogger is a worthwhile add-on.
4. Site access and project duration. Measuring points in the middle of roads with traffic, in restricted areas or far from the site supervision office greatly raise the cost and risk of manual readings. The longer the project and the more frequent the readings, the sooner an automatic system breaks even.
5. Requirements of the owner and relevant authorities. Many projects already specify the monitoring method and reporting frequency in the contract or in the construction permit conditions. Check these requirements before planning the budget.
In practice, most projects settle on a hybrid approach: automatic monitoring only at critical sections and for instruments that can be connected, periodic manual reading for the remaining points, and staff taking manual check readings against the system's values from time to time. This is the best way to catch sensor drift, and it is why an automatic system has never fully replaced site visits.
What Services Does SPN Offer, and How Much Do They Cost?
SPN provides both forms of monitoring, from planning the measuring-point layout with the design engineer, supplying and installing instruments, taking baseline and periodic readings, and processing them into graphs and reports, to installing dataloggers with cloud data transmission and setting alert thresholds by SMS, Line and email based on the values specified by the design engineer. Every report is certified by a licensed civil engineer (COE license) with signature and registration number, and can be used for submission to the relevant authorities. See the full scope of work on the instrumentation and monitoring services page
Instruments within our service scope that can be connected to an automatic system include vibrating wire piezometers, strain gauges, tiltmeters and in-place inclinometers. Instruments read by staff include settlement plates and settlement markers, observation wells and standpipe piezometers, as well as probe-type inclinometers.
Fees depend on the number of measuring points, sensor types, monitoring duration, number of reading rounds and the chosen data transmission method, so they are estimated per project. Contact us for a free quotation within 24 hours. Prices exclude travel and equipment mobilization costs, which are charged according to the distance to the site.
This content explains the principles of comparing manual and automatic monitoring for general understanding. The choice of monitoring method, the type and number of sensors, the reading frequency, the alert threshold for each level and the measures to take when readings exceed thresholds must be specified by the design engineer and the engineer in charge according to the specific conditions of each project.