Technical Note

Output Signal Adjustment and Temperature Compensation

for Honeywell Basic Board Mount Pressure Sensors:

TBP Series–Compensated/Unamplified

NBP Series–Uncompensated/Unamplified

Sensing and Control

1.0 INTRODUCTION

Honeywell offers a broad range of board mount pressure sensors

including fully amplied and compensated, compensated, and

Series and SSC Series.

• Compensated: These sensors provide part-to-part inter

changeability, calibration, and temperature compensation.

An example is Honeywell’s TBP Series. Compensated sensors,

however, may require the use of amplication circuitry,

assuming that an ASIC (Application-Specic Integrated Circuit)

with a mV input ADC (Analog to Digital Converter) is not

being used. Examples of useful amplication circuitry that can

be used with the TBP series can be found in Section 4.0.

• Uncompensated: These sensors provide raw sensor output

datasheets for the TBP and NBP Series Basic Board Mount Pres-

sure Sensors for the Leadless SMT pinout.

Figure 1. Basic Board Mount Pressure Sensors: TBP and

NBP Series

2.0 OUTPUT SIGNAL ADJUSTMENT: SETTING NULL

OFFSET TO ZERO (NBP SERIES)

The NBP Series–Uncompensated/Unamplied has a wide toler-

ance on null offset and span and do not include temperature

compensation. The following procedures can be used to set the

null offset and span to the desired output values and to compen-

(supply) to lead 2 (negative output). Expect values around

300 kOhm (Figure 3).

Figure 2. Negative Null Offset Circuit

Figure 3. Positive Null Offset Circuit

4

1

3

NBP Series

NBP Series

Sensor

in value with an increase in temperature and this adds to the

temperature error. As the resistance in the Wheatstone bridge

increases, the current through the resistors decreases, further-

ing the error due to the inherent decrease in sensitivity in the

pressure sensor. To counter the effect of the resistance change

over temperature, a constant current source excitation instead of

voltage excitation maybe used to reduce the temperature error.

There are a number of ways of generating a constant current for

the current excitation. Figures 5 and 6 show several methods of

supplying a 1.5 mA of constant current to the device.

Sometimes the need arises to ensure that the sensor will respond

to increasing positive pressure (monotonically), whether connect-

ed to an op-amp (operational amplier), instrumentation amplier,

or an input to an ADC.

If the null offset from the sensor is not corrected, a negative null

offset could drive the instrumentation to the ground rail until the

input pressure is enough to counteract this effect. If this occurs,

it means that the sensor will not give a pressure readout in the

lower pressure ranges.

In order to avoid this, the worst case null offset along with the null

-3 mV (-38 mV) when using a 5 Vdc supply.

Setting the offset so that it is always positive can be accom-

plished by placing a resistor between Pins 1 (supply) and Pin

4 (positive output) as shown in Figure 4. The worst-case value

needed to do this is 95.3 kOhm based on the above conditions.

This is a worst-case value for all of the NBP Series; therefore,

in some cases, this might actually drive the offset positive by as

much as 80 mV.

Figure 4. Always Positive Null Offset Circuit