Data Sheet

2 Fluke Corporation Fluke 750P Series Pressure Modules
Pressure module performance
and technology
Fluke 750P Series pressure modules are highly
accurate, with specifications that apply from 0 °C to
50 °C (32 °F to 122 °F), a feature that sets them apart
from other pressure calibrators. Many ranges have
total uncertainties of 0.04
% of full scale and reference
uncertainties of 0.01
% of full scale (see specification
table).
This performance is possible through the innova-
tive application of mathematics and micro-processor
power. Fluke pressure modules have silicon piezo-
resistor sensors which consist of a resistive bridge
fabricated in a silicon diaphragm. Pressure applied to
the diaphragm causes a change in the balance of the
bridge which is proportional to the applied pressure.
The bridge balance change is not linear and is very
sensitive to temperature. However, since these effects
are quite stable with time and with repetitive changes
of condition, the sensors are carefully characterized.
During manufacture, Fluke pressure module sensors
are characterized by reading temperature and pressure
at multiple points. A least-squares regression is used
to calculate the coefficients of a polynomial expression
for pressure. The coefficients, unique to that pressure
module, are stored in the module’s memory.
Each module has its own microprocessor, allowing
it to run the measurement circuitry and to commu-
nicate digitally with a calibrator. When connected to
the calibrator, the modules coefficients are uploaded
from the pressure module to the calibrator. Then, as
pressure measurements are made, raw sensor values
for pressure and temperature are digitally loaded to
the calibrator, where the raw sensor values and coef-
ficients are manipulated to derive and display the
pressure reading.
This innovative technique provides several benefits:
1. Digital communication eliminates errors due to poor
connections and electrical interference.
2. The modules are inherently temperature-
compensated from 0 °C to 50 °C (32 °F to 122 °F).
3. The modules are fully interchangeable because
all measurements are completed in the pres-
sure module itself and then communicated to the
calibrator in digitized form. Modules are calibrated
independently of the calibrator, and can be used
with any 740, 750 or compatible 720 or 710 series
calibrator. Each module has its own serial number
to maintain independent traceability.
Sensor protection in isolated modules
Many of these modules (see table) incorporate a stain-
less steel diaphragm to isolate the sensor. With these
modules, any medium that is compatible with stainless
steel can be used on the high side of the module.
Rugged construction
A urethane overmolding protects against shock if a
module is accidentally dropped and also seals against
dirt, dust, and moisture. Pressure connections are
1
/
8
” NPT female connection. A ¼” NPT Male, ¼” BSP/
ISO and M20 male adapter are also provided with each
pressure module.
Convenient setup
A one-meter cable between the pressure module and
calibrator reduces the length of connecting tubing to
the pressure source. The remote pressure head also
provides an extra margin of safety and convenience
by removing the calibrator and operator from the
pressure source in the event or need for semi-remote
measurements.