Level Measurement · Hydrostatic Level Transmitters
Submersible hydrostatic level transmitter for water tanks, sumps, reservoirs and pits, from 1 m to 10 m as standard, with a probe rated IP68.
XK-136P ·
A submersible level transmitter is the direct answer to a level measurement, and it is the one that asks least of the vessel. The probe is dropped into the liquid on the end of its cable and read; there is no mounting to arrange, no alignment to set and no clear path to keep open. What it asks for instead is a liquid whose density is known and stable, and a vessel it can be lowered into.
It is also the one of the three common level technologies that does not care what the surface is doing, which is what makes it the instrument for a sump, a pit and a river gauge.
The measurement is the pressure at the bottom of the vessel. A column of liquid exerts a pressure at its base that rises in proportion to its depth, the density of the liquid and gravity, so a sensor resting on the bottom sees a pressure that tracks the level directly. The transmitter converts that pressure into a level once it has been told the density of the medium.
That single sentence contains both the strength and the weakness of the type. The strength is that pressure is indifferent to foam, vapour, condensation, a slopping surface and everything else that troubles a non-contact instrument. The weakness is that the conversion depends on the density, so the level reported is only as good as the density assumed. A tank that sometimes holds water and sometimes a process fluid, or a liquid whose density moves with temperature, will give two different levels from one pressure reading.
The probe has to be referenced to something, and the atmosphere is what it is referenced to. A tube inside the cable runs from the sensing element to the terminal, where it is left open to air, so that the measurement is a gauge pressure rather than an absolute one. Without it the instrument would read the pressure of the headspace as well as the depth of the liquid, and the reading would move with the barometer.
That makes the cable part of the instrument rather than an accessory, which is why the material supplies a cable length matched to the range and why the vent tube is worth protecting during installation. A kinked, pinched or flooded tube produces a level reading that drifts for reasons invisible at the instrument, and it is one of the few failure modes the installer introduces rather than the process.
The range is chosen from the depth to be measured, and the useful test is not the maximum depth but the normal level: a range far larger than the duty uses only a fraction of the instrument’s span and gives away resolution that was paid for. The material offers standard ranges from one metre to ten metres, with the current-output form available to 100 m and a special construction to 500 m.
The probe is then matched to the medium. The standard wetted materials are a 316L diaphragm in a 304 stainless housing on a rubber cable, which suits water, wastewater and oils. Where the medium would attack them, the material offers an anti-corrosion version, and where the temperature exceeds the standard limit it offers a high-temperature version. Because the probe is immersed permanently, this compatibility question is decided before range or accuracy, not afterwards.
The material gives three ways of fixing the probe, and the choice between them is about the water rather than about the instrument. Direct immersion suits static, clean liquid: the probe is lowered to just above the floor and the cable secured above the surface. A perforated stilling pipe is the answer in a dirty or fast-moving sump, where it keeps solids away from the ports and removes the effect of waves and velocity. A perforated fixing block on the floor is the third, for a flow strong enough to move the probe, since a probe that is not vertical and still does not read the head of liquid above it.
That concern is the practical one for this type. A reading that moves with the flow rather than with the level is usually an inlet discharging onto the probe, and the material offers three specific remedies for it: reshaping the inlet so the stream breaks into droplets, turning the inlet upward so the water spends its energy in the air, or shielding the probe inside a perforated pipe.
The limitations follow from the principle. A single gauge transmitter cannot be used in a sealed or pressurised vessel, because there is no atmosphere to reference against and the headspace pressure would be added to the reading; a differential arrangement is the answer there. The reading is only as good as the density assumed, which matters in a tank that holds more than one product. And the probe has to be compatible with the medium for the whole of its life, since it is immersed continuously rather than occasionally.
The material also leaves several figures unsettled. The working temperature is given two different ways in the same document, from -10 to 40 °C in the table and -20 to 40 °C on the order cards. The accuracy is given as a class in one place and as a resolution percentage in another, which are different quantities. The overload rating is given as a percentage without a time. And the control instrument’s outputs are stated as four relays with no analogue or communication output given.
The items that fix the answer are the medium, its density and whether either changes; the maximum depth and the lowest and highest levels in service; whether the vessel is open to atmosphere; the chemical compatibility of the wetted materials and any cleaning agents the probe will meet; the medium and ambient temperatures, working and extreme; the range and the cable length, which are ordered together; the output required and what will read it; whether the installation only measures or also drives a pump or an alarm; and how the cable will be run and glanded. A tank description and the medium are enough for a covering quotation. Quantity, destination port and required delivery date complete the enquiry.
Every value below is taken from source documentation. Where a parameter is not stated in the available material it is marked as information required rather than estimated.
| Range | 0 to 1 m, 0 to 3 m, 0 to 5 m and 0 to 10 m as standard, and to 500 m to orderStandard |
|---|---|
| Accuracy | 0.5 class, with 0.2 class to order; the order cards also quote a resolution of 0.5 %, which is a different quantity from an accuracy class and is not reconciled with it in the materialInformation required |
| Annual drift | ±0.2 % of full scaleStandard |
| Overload | 150 %Standard |
| Response time | T90 ≤1 msStandard |
| Temperature compensation | 0 to 40 °CStandard |
| Repeatability | Not stated in the materialInformation required |
| Output | 4-20 mA as standard; 0-5 V and RS-485 to orderStandard |
|---|---|
| Supply | 24 V DCStandard |
| Wiring, current output | Two-wire, one conductor carrying the supply and one carrying the signalStandard |
| Wiring, voltage output | Three-wire, with a common conductor in addition to the supply and signalStandard |
| Control instrument relays | Four relay contacts; no analogue or communication output is stated for the instrumentStandard |
| Control instrument supply | 220 V, with a 24 V feed to the transmitterStandard |
| Cable length against range | 5 m of cable for ranges up to 5 m, and a cable equal to the range for 6 m and aboveStandard |
| Output against range | The 4-20 mA form is offered from 1 m to 100 m; the RS-485 form is offered from 1 m to 15 mStandard |
| Wetted materials | 316L stainless diaphragm, 304 stainless housing and a rubber cableStandard |
|---|---|
| Probe dimensions | 26 mm diameter by 110 mm longStandard |
| Sealing | Multi-stage sealing and a double waterproof construction, described in the materialStandard |
| Pressure ports | Four ports in a sloped arrangement, described as designed not to blockStandard |
| Cable | Flexible and waterproof, shielded, with a vent tubeStandard |
| Ingress protection | Probe IP68, assembly IP65Standard |
| Working temperature | The material gives -10 to 40 °C in its table and -20 to 40 °C on the order cards, and both are carriedInformation required |
| Medium temperature | -20 to 40 °C on the order cards; the material states that a higher temperature requires a special versionStandard |
| Storage temperature | Not stated in the materialInformation required |
| Panel size | 160 × 80 mm, with a 152 × 76 mm cutout and an 84 mm depthStandard |
|---|---|
| Display | A light column and a digital reading togetherStandard |
| Alarm settings | Four points, described as high, high-high, low and low-lowStandard |
| Keys | Set, increase, decrease and shift, with a mute switchStandard |
| Functions | Level display, level alarm and level controlStandard |
| Control arrangement | The material shows a fill arrangement in which a valve is opened on a low level and closed on a high one, and the same instrument controlling a drainStandard |
| Scope | Additional forms supplied in November 2026 for this product type. Figures below are from that batch; where they differ from the rows above, both are recorded rather than merged.Standard |
|---|---|
| Ranges in this batch | 0 to 1 m, 0 to 5 m, 0 to 10 m and 0 to 20 mStandard |
| Output | 4-20 mA, RS-485/Modbus, 0-10 V and 0-5 V all appear; RS-485 is the most common in this batchStandard |
| Supply | 24 V DC as the main form, with 12 V DC and battery-powered versions also listedStandard |
| Process connection | Threaded, flanged and M20 x 1.5 versionsStandard |
| Wetted materials | 316L stainless diaphragm and 304 stainless body, with polyurethane or PTFE cable and ceramic-capacitor sensing elementsStandard |
| Ingress protection | IP68 at the probeStandard |
| Model | Configuration | Key ranges | Availability |
|---|---|---|---|
| XK-136P | Submersible hydrostatic level transmitter with a 316L diaphragm in a 304 stainless housing, on a vented cable, with voltage and serial output options | 0 to 1 m, 0 to 3 m, 0 to 5 m and 0 to 10 m as standard, to 500 m to order; 0.5 class, 0.2 class to order; 4-20 mA; 24 V DC; probe IP68 and assembly IP65 | One transmitter model. The control instrument offered alongside it carries no model designation in the material, so it is recorded under customisation rather than as a second model row |
Certifications are only published once a certificate copy can be produced, so this section is deliberately empty rather than populated with assumed approvals. Tell us which approvals your application requires and we will confirm what is available for this instrument.
The following are required for a complete specification but are not stated in the documentation supplied to us. They are listed rather than estimated:
The medium and its density first, because the instrument measures pressure and converts it to a level using that density, so a tank that holds different products or a liquid whose density moves with temperature will not give a level from one calibration. Then the depth to be measured, which fixes the range and shows how much of full scale the normal level uses. Then whether the vessel is open to atmosphere, since that decides whether a vented reference is enough or a differential arrangement is needed. Then the temperature, the chemical compatibility of the wetted materials, and whether the reading has to do anything - fill, empty or alarm - rather than only be displayed.
It keeps the sensor referenced to the atmosphere. The element inside the probe measures the pressure of the liquid above it, and without a reference it would also be measuring the pressure of the air in the vessel headspace and the barometric pressure of the day, so the reading would move with the weather. The vent tube runs inside the cable to the terminal, where it is left open to air, which makes the measurement a gauge pressure and therefore a level. It is also the one part of the installation that an installer can easily ruin, since a kinked, pinched or flooded tube produces a reading that drifts for reasons that are hard to see.
Not as a single gauge transmitter, because a sealed vessel has no atmosphere to reference against and the headspace pressure would be added to the reading. Sealed and pressurised vessels are measured with a differential arrangement that compares the bottom of the tank with the top and cancels the headspace pressure. The form described here is for an open or freely vented vessel, which is the case for almost all of the duties it is bought for - a water tank, a sump, a pit, a reservoir or a river.
Nothing, and that is the advantage of measuring pressure rather than distance. The instrument sits at the bottom and reads the head of liquid above it, so foam, a slopping surface, floating debris and anything turning in the tank leave the reading essentially unchanged. What does disturb it is an inlet discharging directly onto the probe, because that adds velocity pressure to the static head and shows up as a reading that moves with the flow. The answer is a stilling arrangement, a shield or a different mounting point, and the material gives three of them - a perforated pipe, a fixing block on the floor, or reshaping the inlet so the stream does not land on the probe.
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