Honeywell MPR, ABP, and TBP Series Board Mount Pressure Sensors User Guide

Liquid Level Height Sensing UsingSelected Honeywell Board MountPressure Sensors: MPR, ABP, andTBP SeriesA Technical Note


This technical note demonstrates how to calculate the liquid level height in an unpressurized or pressurized container by using a board-mounted pressure sensor to measure the hydrostatic pressure.


The full equation for pressure liquid level height versus pressure is:Liquid Level Height = Pressure Exerted/(Density * Gravitational Constant)However, for most applications at lower altitudes the simplified equation may be used:Liquid Level Height = Pressure/Specific Gravity, or H = P/SG where:H = Height, in inches, of the liquid being measuredP = Pressure, in inches of water (inH2O), of the liquid being measuredSG = Specific gravity constant of the liquid being measured (See Table 1.)Table 1: Approximate Specific Gravity Constants of Common Liquids1

Liquid Specific Gravity Constant
Water at 4°C 1
Water at 20°C 0.998
Ethyl alcohol at 20°C 0.789
Isopropyl alcohol at 20°C 0.785
Seawater at 25°C 1.028


Using an unpressurized container

Using the equation H = P/SG, the two examples in Figure 1 show how different media at different pressures may have the same liquid level height. The pressure sensor shown is Honeywell’s ABP Series, enhanced accuracy, digital or analog output, compensated/amplified, basic board mount pressure sensor. The MPR Series is an I 2 C or SPI digital output sensor.

Figure 1. Two Examples of Finding Liquid Level Height Using an Unpressurized Container

Example 1:Water at 4°C Example 2:Ethyl alcohol at 20°C
  H = 8.5 inH2O/1.00  H = 6.7 inH2O/0.789
  H = 8.5 in  H = 8.5 in

Example 1:

Example 2:

Using a pressurized container

Instead of using a single ported sensor, as was used in measuring the liquid level height in an unpressurized container, the pressure sensor used here needs to be a dual-ported,  liquid media compatible (wet/wet) device. The sensor is mounted at the bottom of the container. This positioning gives a liquid-coupled measurement. Although a small air bubble may be present due to trapped air between the container and sensor, this method, for the most part, directly measures the pressure which indicates the height of the liquid.

Example: What is the liquid level height of a container whereP1 = 9.0 inH20, P2 = 0.5 inH20, and the liquid is water at 4°C?Using the difference between P1 and P2 as P, the equation in Section 2.0becomes: H = (P1 – P2)/SG:H = (9.0 inH20 – 0.5 inH20)/1.00H = 8.5 in

Figure 2. Pressurized Container

Due to the relative unavailability of dual-ported sensors tolerant of liquid media on both ports, two single-ported gage or absolute pressure sensors have traditionally been used  in this situation. This method not only carries the cost penalty of having to buy two sensors instead of one but may also double the measurement error. For this reason, ABP  Series and TBP Series differential sensors are preferred.


Example: What is the required pressure range of a sensor if the maximum height of the container is 25 inches, and the liquid is water at 4°C?Solving for P, the equation in Section 2.0 becomes: P = H x SG:P = 25 in x 1.00P = 25 inH20A 25 inH2O full-scale pressure sensor is used (1 psi ≈ 27.7 inH2O at 4°C), such as the ABP Series liquid media capable sensor ABPANT001PGAA5 or MPR Series  MPRLS0001PG0000SAB as shown in Figure 3.

The ABPANT001PGAA5 sensor provides an analog output proportional to the applied pressure in the container, from 0.5 Vdc (no pressure applied) and 4.5 Vdc (1 psi applied). In this example, the MPRLS0001PG0000SAB the sensor provides an SPI digital output proportional to the applied pressure of approximately 9430370 counts at 16 inches of water from the 24 bit ASIC when the water level is at 16 in.

Figure 3. Known Container Height


This method, as shown in Figure 4, allows the sensor to be remotely mounted using tubing to make the connection between the bottom of the container and the sensor. A  single piece of tubing, or a piece of tubing connected to a tube, is used to run from the bottom of the container to the sensor.The advantage of this method is that the media has an air column between it and the pressure sensor, helping to isolate the sensor from harsh media. A possible concern is that  if the tubing interface or sensor has even a small amount of mechanical leakage, it can have a significant impact on accuracy, which shows up as drift over time of the measurement.

Figure 4 . Remote or Top Mounting


A TBP Series, compensated/unamplified basic board mount pressure sensor with the liquid media option, may be used to measure liquids that are compatible with silicone.  Figure 5 shows an example circuit that may be used to amplify the output.Figure 5. Example Output Amplification Circuit

Example: What is the required value of Rg if P = 27.8 inH2O maximum, the sensor used is 1 psi, and the liquid is water at 4°C? Equations used:Rg = 100000/(Gain-1)Gain = Span/SignalTo account for part-to-part sensor and amplifier offset variation, use a 100 kOhm potentiometer to calibrate Vout:Vout = 0.5 Vdc (no pressure applied)Resulting amplifier output:P at 0 inH2O = 0.5 VdcP at 27.8 inH2O = 4.5 VdcSpan = 4.5 Vdc – 0.5 VdcSpan = 4 VdcTBPDANS001PGUCV full scale output = 1.5mV/V, or 7.5 mV when using a 5 Vdc supply:Gain = 4 Vdc/0.0075 VdcGain = 533Rg = 100000 Ohm/(533 – 1)Rg = 100000 Ohm/532Rg = 188.0 Ohm


SEK002 Sensor Evaluation Kit (See Figure 6)

The MPR Series and digital versions of the ABP Series may be used in conjunction with the SEK002 Evaluation Kit (purchased from Honeywell authorized distributors). The  SEK002 allows the user to obtain sensor readings without needing to develop any code.The SEK002 is plugged in as a shield board to an Arduino™ Uno Rev3 Microcontroller Board. Honeywell evaluation software downloaded to the user’s PC controls the  Arduino Uno Rev3 to take sensor readings that are then displayed on the PC’s screen.

Figure 6. SEK002 Sensor Evaluation Kit (Shown with ABP Series Sensor and Arduino™ Uno Rev3)

MPR Series sensor on breakout board (See Figure 7)

Selected MPR Series sensors (catalog listing contains a “B” suffix) are available mounted on a breakout board which allows easier connection to the SEK002 Sensor Evaluation  Kit.

Figure 7 . MPR Series Breakout Board 

Warranty/RemedyHoneywell warrants goods of its manufacture as being free of defective materials and faulty workmanship during the applicable warranty period. Honeywell’s standard product warranty applies unless agreed to otherwise by Honeywell in writing; please refer to your order acknowledgment or consult your local sales office for specific warranty details. If warranted goods are returned to Honeywell during the period of coverage, Honeywell will repair or replace, at its option, without charge those items that Honeywell, in its sole discretion, finds defective.The foregoing is the buyer’s sole remedy and is in lieu of all other warranties, expressed or implied, including those of merchantability and fitness for a particular purpose. In no event shall Honeywell be liable for consequential, special, or indirect damages.While Honeywell may provide application assistance personally, through our literature and the  Honeywell website, it is the buyer’s sole responsibility to determine the suitability of the product in the application.Specifications may change without notice. The information we supply is believed to be accurate and reliable as of this writing. However, Honeywell assumes no responsibility for its use.

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