Conditions for Using 24VDC Level Sensors in Humid Environments

Whether a 24VDC level sensor can be used in a humid environment over the long term cannot be determined solely by its supply voltage. 24VDC is a common safety extra-low voltage level in industrial measurement and control systems, making it convenient for use with PLCs, digital display control instruments, variable frequency drives, and remote data acquisition modules. However, this does not mean that the sensor is inherently waterproof. Factors that truly determine whether the equipment can operate reliably include the enclosure protection rating, probe sealing design, cable outlet structure, junction box sealing, medium corrosiveness, and on-site installation location.

In applications such as food cleaning areas, wastewater tanks, condensate tanks, underground pump rooms, and around chemical storage tanks, air humidity is often close to saturation. Sensors may also be affected by condensation, splashing wash water, or long-term immersion. If a standard product with a non-sealed enclosure is selected, moisture entering the circuit board or wiring chamber can easily cause reduced insulation resistance, signal drift, output fluctuations, or even short-circuit damage in severe cases.

For industrial sites requiring continuous level monitoring, it is recommended to first check protection ratings such as IP65, IP67, or IP68, while also confirming the specific limitations stated in the product manual regarding immersion depth, duration, medium temperature, and cable resistance. Shaanxi Qinkong Sensor Technology Co., Ltd. can provide suitable level measurement and control products based on tank structure, liquid properties, signal interfaces, and installation dimensions, avoiding judgments of moisture resistance based solely on appearance.

How to Assess Protection Ratings, Sealing Structures, and Installation Locations

Different Humidity Levels Require Different Protection Levels

An IP protection rating consists of two digits. The first digit mainly indicates protection against solid foreign objects, while the second digit indicates water resistance. For highly humid air in general workshops, IP65 products can usually meet basic operating requirements. For equipment areas exposed to cleaning water, the spray direction, pressure, and duration should be further confirmed. Where probes, cable connectors, or integrated transmitters need prolonged contact with liquids, IP67 or IP68 ratings should be considered.

It should be noted that IP67 normally applies to temporary immersion and does not mean that the device can remain submerged indefinitely. The specific immersion capability of IP68 is also not standardized: some products may only allow immersion to a depth of 1 m, while certain customized products can be designed for 5 m, 10 m, or even greater ranges. Therefore, during procurement, the “protection rating” and the “permitted immersion conditions” should be confirmed separately.

In addition to the product itself, overall sealing after installation is equally critical. Even if a sensor meets IP68, moisture may still enter the system through cables or connectors if intermediate cable joints are exposed, junction box covers are not tightened, or suitable sealing components are not used on threaded interfaces. During engineering acceptance, the sensor, connectors, conduits, and control cabinet cable entry points should be inspected as one complete protection chain.

Sealing Materials Must Match the Liquid Medium

Not all “water” in humid environments is neutral clean water. Cleaning solutions used in food production may contain acidic or alkaline components; wastewater may contain oil, salts, and suspended solids; and chemical liquids may corrode 304 stainless steel, standard rubber, or PVC cables. The wetted materials of the level sensor, O-ring material, diaphragm material, and cable jacket should all be included in the selection process.

Common stainless steel probes are suitable for most water-based media. However, for liquids with high chloride ion content, strong acids or alkalis, or high temperatures, the suitability of materials such as 316L, Hastelloy, and PTFE should be further evaluated. Seals must not be overlooked either: NBR, FKM, and EPDM differ in oil resistance, high-temperature resistance, and acid and alkali resistance. Incorrect material selection can cause seal aging, swelling, or cracking.

If the medium is viscous, prone to crystallization, or highly adhesive, deposits may form on the sensor probe surface and slow the level response. For such projects, the medium name, concentration, temperature, viscosity, vessel pressure, and installation port dimensions should be provided in advance, so that technical personnel can determine whether hydrostatic, submersible, capacitive, radar, or another more suitable measurement solution should be used.

Moisture Protection Considerations for 24VDC Power Supply and Signal Wiring

Stable Power Does Not Necessarily Mean Stable Signals

Common outputs for 24VDC level sensors include 4-20mA, 0-10V, RS485, and relay switching outputs. For 4-20mA two-wire products, power supply and signal generally share one pair of conductors, providing simple wiring and good interference resistance, making them suitable for industrial sites with longer transmission distances. Four-wire products generally separate the power supply and output circuits, facilitating connection to various signal types, but requiring relatively more wiring.

In humid areas, shielded cables that meet on-site requirements are recommended, and the cable outer sheath should be kept intact. The shield should generally be grounded at one end in accordance with the system grounding principle to avoid ground loop interference. Sensor signal cables should be kept at a reasonable distance from 380V power cables and variable frequency drive output cables; in common engineering practice, a distance of at least 300mm can be reserved. Where crossing is unavoidable, the cables should cross at an angle close to 90 degrees.

Junction boxes and control cabinets are common locations for moisture ingress. Cables entering a junction box should form a naturally hanging drip loop to prevent condensation from flowing directly into the box along the cable. After terminal crimping, the tightness of cable clamping and the exposed copper wire length should be checked. For outdoor or underground environments, waterproof connectors, potted connectors, or sealed conduits may be used according to operating conditions.

Can a Relay Output Directly Control a Water Pump

A level sensor with relay output can serve as a start-stop control condition, but it cannot be assumed to directly drive all water pumps. The rated voltage, current, and load type of the relay contacts must first be confirmed. For example, small control circuits may be connected directly through sensor contacts, whereas the starting current of higher-power motors may far exceed the contact capacity of the sensor.

For common AC water pumps, a more reliable approach is to use the level sensor relay output to control an intermediate relay, an AC contactor coil, or a PLC input point, and then use a dedicated motor control circuit to drive the pump. This reduces the risk of contact burning and also facilitates functions such as manual/automatic switching, dry-run protection, high- and low-level interlocking, and fault alarms.

In humid environments, the control cabinet should also be equipped with reliable grounding, circuit breakers, residual current protection, and surge protection measures. For drainage pumps that start and stop frequently, it is recommended to set a reasonable level differential to prevent repeated level fluctuations at the threshold from causing short-cycle pump operation, thereby extending the service life of sensors and actuating equipment.

Compliance Requirements for Food, Coal Mine, and Complex Operating Conditions

What Certifications Are Required for Food Level Sensors

For the food industry, the key requirements for level sensors are the safety of wetted materials, hygienic structural design, and process traceability. When used in applications such as beverages, dairy products, condiments, and auxiliary pharmaceutical processes, particular attention should be given to whether wetted parts use materials suitable for food-contact environments, whether surfaces are easy to clean, and whether the sealing structure has dead zones where residues may accumulate.

The specific certifications required should be determined by the product application, customer system, and export destination requirements. Domestic projects may focus on material certificates, test reports, hygiene-related requirements, and company quality management documentation; export projects or projects for particular customers may also require CE, RoHS, FDA material compliance, or other industry documentation. Purchasers should avoid simply asking whether certifications are available and should instead clearly identify the medium and process stage in which the final equipment will be used.

For tanks requiring CIP cleaning or high-temperature disinfection, in addition to food-contact compliance, the sensor temperature resistance range must also be confirmed. For example, level measurement products intended for normal-temperature applications may not necessarily withstand cyclic cleaning above 80℃, let alone be used directly under high-temperature steam sterilization conditions. Specifying the operating temperature, cleaning temperature, and peak instantaneous temperature separately in the technical agreement can reduce subsequent application disputes.

Must Coal Mine Safety-Certified Level Sensors Have a Coal Mine Safety Certificate

If a level sensor is used in locations subject to safety mark management under national regulations, such as underground coal mines, products with the corresponding coal mine safety mark qualifications generally need to be selected in accordance with on-site regulatory requirements. Coal mine safety requirements are not a substitute for standard industrial waterproof ratings; they also focus on explosion protection type, electrical safety, applicable environments, and product market access scope.

When selecting a product, the project leader should first confirm whether the installation location is above ground or underground, whether it is classified as an explosive environment, whether connection to a mining monitoring system is required, and the local mine's requirements for product catalogs and certificate validity periods. Descriptions such as “waterproof,” “24VDC,” or “industrial grade” alone cannot determine whether a product meets market access requirements for mining sites.

For other hazardous locations involving chemicals, oil and gas, dust, and similar conditions, the explosion protection rating and installation method should likewise be confirmed according to area classification, medium characteristics, and system specifications. For level interlocks related to production safety, it is recommended that the design organization, equipment supplier, and on-site safety management personnel jointly verify the technical documentation to ensure that product parameters are consistent with actual operating conditions.

Installation, Maintenance, and Customization Recommendations for Humid Operating Conditions

Avoid Standing Water, Condensation, and Probe Blockage

Before installation, confirm that the measuring range matches the actual liquid level height. For submersible level sensors, for example, the probe should be suspended above the bottom of the tank to avoid direct contact with sludge, sand, or sediment; a distance of 100mm to 300mm can generally be reserved according to tank conditions. If the probe is placed too close to the tank bottom, it can easily become buried by sediment during long-term operation, resulting in excessively high measured values or no response.

For viscous liquids, slurries, oils, greases, or crystallizable media, blockage prevention should not rely solely on frequent manual cleaning. Depending on the medium characteristics, a flush diaphragm structure, larger installation port diameter, bypass pipe, or guided-wave structure may be selected, while the measuring surface should be kept away from the material inlet impact area wherever possible. Where the process permits, a periodic flushing connection can be installed to reduce the impact of material buildup on measurement results.

Routine inspections can be conducted monthly or according to the on-site maintenance cycle, with focus on abnormal fluctuations in displayed values, damage to cable sheaths, water seepage at sealed connectors, and deposits on the probe surface. For 4-20mA signals, the on-site displayed value and PLC acquisition value can be compared under stable level conditions. If the deviation continues to increase, the power supply, wiring, installation position, and calibration status should be checked promptly.

How Should the Lead Time for Customized Level Sensors Be Scheduled

The delivery lead time for customized level sensors depends on the measuring range, probe length, output type, wetted material, thread or flange dimensions, protection requirements, and whether special calibration is needed. Products with standard ranges, commonly used 4-20mA outputs, and standard stainless steel structures can generally be arranged relatively quickly according to inventory and production schedules. Where special cable lengths, high-temperature-resistant materials, non-standard flanges, or complex medium compatibility are involved, more time should be reserved for confirmation and testing.

To shorten the communication cycle, purchasers should provide the medium name, maximum temperature, vessel pressure, measuring range, installation method, supply voltage, output signal, accuracy requirements, cable length, and photographs of the operating environment at one time. The more complete the information, the easier it is to identify moisture protection, corrosion resistance, interference resistance, and mechanical installation risks at an early stage, avoiding further structural changes after sample confirmation.

Leveraging its brand operation, sales, and technical service system, Xi'an Shenghongchuang Instruments Co., Ltd., together with the production and testing capabilities of Shaanxi Qinkong Sensor Technology Co., Ltd., can provide level sensor selection, non-standard customization, signal integration, and technical support for projects in machinery manufacturing, chemical energy, logistics and warehousing, environmental monitoring, and automated production lines. After submitting on-site medium information, measuring range, installation port details, and control system parameters, the appropriate protection rating, sealing solution, and delivery configuration for humid environments can be further confirmed.