a Baker Hughes business

PACE CM3

Where speed and accuracy combine

druck.com

Introduction

Druck, a Baker Hughes business, has beendeveloping and delivering pressure measurement
solutions to customers for more than 40 Years, across
many applications in Aerospace, Oil & Gas, Industrial,
Metrological Laboratories and many others. One of
Druck’s main areas of technical expertise is Pressure
Controllers. These are used in many different industrial
applications and by metrological laboratories ascalibration standards around the world.
Druck’s PACE pressure controllers are widely recognised as the world’sfastest, with the ability to fill and control volumes of 300cc in under
5 seconds.
Druck, has beendeveloping anddelivering pressure
measurement

solutions for morethan 40 years

As Druck’s proprietary sensing technology known as TERPS (Trench
Etched Resonant Pressure Sensor) has evolved, Druck has planned theexpansion of the PACE platform, in particular increasing the pressure
range of the PACE control modules by adding to the already successful
CM3 high accuracy pressure controller modules. This paper focuses on
the introduction to the market of new pressure controller modules in theCM3 range and what their performance will mean for Druck’s customers.
Druck is expanding its PACE CM3 control modules from the alreadysuccessful 2 bar and 3.5 bar absolute products to include newpressure ranges. Druck has recently released new absolute pressure
controller ranges of 8, 11, 21, 36 and 71 bar and the associated pseudo
gauge controller ranges 7, 10, 20, 35 and 70 bar. Druck will continue
the development of future pressure ranges, with up to 211 bar absolutepressure planned for release during 2021.

2

PACE CM3 will utilise Druck’s established TERPS® (Trench Etched Resonant
Pressure Sensor) technology at its core, which delivers unprecedented
metrological characteristics and resultant levels of performance forPACE controllers.
This paper will present the main attributes of PACE CM3 enabled pressurecontrollers and resultant performance, namely:
Druck’s PACE

pressure controller iswidely recognised as
the world’s fastest•	TERPS® technology•	Accuracy and its factors•	Long Term Stability•	Pressure controlling abilities•	PACE’s modular construction using control modules such as PACE CM3•	Automated calibration and data integration using Druck’s
4Sight2 software•	Customer support and service
Druck’s philosophy is to provide customers with solutions aligned
to their needs, where specifications meet customers’ requirements
and to provide openness and transparency concerning the company’sinstruments’ capabilities.

enhanced with ourTERPS technology inside

3

TERPS® TechnologyTERPS® relies on the straining of a resonant structure to change
the frequency of the transducer, which is proportional with the pressure
applied onto the sensor’s diaphragm. The unique design of TERPS® is thebase of its great performance, especially in terms of drift and hysteresis(pressure & temperature).

Pressure

The unique designof TERPS® is thebase of its greatperformance

RPT Die
Isolation DiaphragmPressure connector

Figure 1: Isolated TERPS configuration

The TERPS® structure and build has the following characteristics:
The TERPS® structure and build has the following characteristics:•	Well defined resonant frequency by using Silicon-on-Insulator (SOI)
Well definedresonant
frequency
by usingthe
Silicon-on-Insulatorto•	control
thicknessand massof resonatingstructure;(SOI)
tocontrol
thicknessandmassofresonatingstructure;•	Insensitive to media viscosity by using deep reactive ion
etching•	Insensitive
towellmedia
viscosity
by structuresusing deepfor
reactiveionmass
etching(DRIE)
to create
definedpatentdynamic
create well defined patent structures for dynamicand(DRIE)
force tobalance;mass
andisolation
force balance;•	Harsh
media
by using DRIE to manufacture complex•	Himpedancearsh mediasensing
isolationtechnique;by using DRIE to create a complex
lowimpedance
sensinghysteresis
technique;•	Lowlow
thermaland pressureby using silicon fusion•	Low thermalbonding(SFB) and pressure hysteresis by using silicon
fusion bonding (SFB)

4

PACE CM3 High Accuracy Pressure Controller

The entire TERPSstructure ismechanicallyand dynamicallybalanced

External pressure deflects the resonator
Figure 2: Isolated TERPS configuration

The whole structure (diaphragm and resonator) is mechanically anddynamically balanced to ensure that as pressure (i.e. strain) is applied,the change in frequency occurs in a continuous manner, without signal
discontinuities. This is particularly important in providing the highprecision of the transducer and whilst Druck quote precision as
15 ppm FS on the product datasheet, many of the Druck’s TERPS
outperform this specification.

Accuracy
As per the VIM (Vocabulaire International de Métrologie) definition,accuracy is a qualitative term, defined as “closeness of agreement
between a measured quantity value and a true quantity value ofa measurand”.

Accuracy isdefined as‘closeness ofagreement
between ameasured
quantity value
and a true
quantity value ofa measurand’

The term “accuracy” should be associated with the specified
measurement error, including the impact of systematic error, random
error and drift (in cases where accuracy is specified over a defined timeperiod). Definitions of accuracy should consider the application and theneeds of the customer.
The following is a typical expression of accuracy for Druck’s PACE
pressure controller with a TERPS-enabled PACE CM3 control module
incorporated within the instrument:
Precision =+/-15ppm FS (error to the calibration standard)
Calibration expanded uncertainty (sigma=2) = +/- 0.0022% of rdg
Drift = +/- 25ppm FS/year (2 & 3.5 bar a)+/- 10ppm FS/month when zeroed 8-211 bar
Note: The above 3 factors are uncorrelated and follow normal distributions.

For the new PACE pressure ranges Druck achieves an accuracy of+/-11ppm rdg + 26ppm FS with a 95.45 % confidence interval (k=2).
However extensive testing suggests PACE shows the potential to performconsiderably better than this quoted value.
5

PACE CM3 High Accuracy Pressure Controller

Regarding accuracy, other manufacturers’ instrumentation may bedefined in alternate methods which have subtle implications for the user.
For example:
Definitions ofaccuracy should
consider theapplication andthe needs ofthe customer

Manufacturer A expresses accuracy as:
80ppm rdg down to 33%FS then 80ppm of 33%FS
Manufacturer B expresses accuracy as:
100ppm rdg or 30ppm %fs whichever is the greater.
Figure 3 demonstrates how Druck’s PACE performs when comparing
accuracy against other Pressure Controller manufacturers. Further
accuracy improvements can be made on a PACE6000 if utilising theauto-ranging feature in conjunction with two appropriately ranged
control modules
Pressure Measure Accuracy Comparison

0.012Uncertainty %
0.01

0.008

0.006

0.004

0.002

0% FSR
01020

Druck CM3304050

Manufacturer A

607080

Manufacturer B

90100Figure 3: PACE expanded uncertainty comparison as % of range

DriftDrift is a very important metrological characteristic, as it will often dictate
the accuracy of the instrument between two successive calibrations,which involves both time and cost for the user.
The graph in Figure 4 represents the typical drift for Druck’s TERPS® forthe 2 bar absolute pressure range and compares its drift performanceover time against the drift performance claimed and achieved by otherinstrument manufacturers. Whilst Druck’s specification includes a 25 ppm
FS drift per annum, the achieved drift performance over time of TERPS®, inmany cases is much better than the stated specification.

[ Drift will often dictate theaccuracy of the instrument ]6PACE CM3 High Accuracy Pressure Controller1201008060
40
200-20

Druck has
introduced
an innovative
method of taring
the drift against
a highly accurate
barometric sensor

050100150250300350400

TERPS Drift ppm FS
Typical Piezoresistive Sensor Drift Spec ppm FS
Claimed Piezoresistive Sensor Drift Spec ppm FS
Figure 4: TERPS® drift performance versus competitor’s specifications

Both 2 & 3.5 bar absolute exhibit similar behaviour in terms of drift
performance. However, for ranges of 8 bar absolute pressure and above,
Druck has introduced an innovative method of taring the drift against
a highly accurate barometric sensor, which is included in all Druck’s
PACE CM3 control modules. As with all other factors, the uncertainty
contribution of taring PACE CM3’s main range against the barometricsensor is included in the expanded uncertainty evaluation (accuracy).
Figure 5 below assumes a typical case scenario where the barometerhas an expanded uncertainty of 10 Pa (through good calibration 5 Pa
is achievable) and it shows that at 71 bar range, the contribution will
become negligible (~1 ppm FS).
15

Tare

to at
unce mosphe
ric prtain
rety contrib ssure expaution[ppm ndedFS]

Influence of taring [ppm FS]

10The buyer should
investigate
whether theaccuracy value
stated in themanufacturer’sspecification
includes drift

200Days50-5-10-15

811213671

Absolute Pressure Ranges [bar]Figure 5: Expanded uncertainty contribution of taring by pressure range

Before purchasing a pressure controller, the buyer should investigate
whether the accuracy value stated includes drift for the recalibration period.
If not, then the accuracy figures stated is valid only at the point of calibrationand not over the course of time between calibrations. Knowing this will helps
the end user to calculate the total cost of ownership of their instrument.

7PACE CM3 High Accuracy Pressure Controller

Control Stability and Offset Importance
When a pressure controller is used in an automated calibration system,
the time taken to get to the setpoint and stabilise is often critical inachieving increased flow through the production line without sacrificing
accuracy. Druck’s PACE pressure controller is the market leader in time
taken from command to setpoint, because of the advanced pressure
control algorithm.
Once the controller has stabilised controller noise and offset will also
impact the speed of measurement taken. When the controller is ‘noisy’,readings must be averaged over a period to reduce the peak error thatwould otherwise impact the uncertainty budget.

The PACE product isthe market leader
in time takenfrom command
to setpoint

Controller noise can only be averaged out if the noise signal is random
and evenly distributed either side of the aim value. If the controller has a
non-random deviation, then the measured signal can be in error due toaliasing leading to an offset in the signal. Care must be taken if averaging
poor controllers with high noise values. The best method is to reduce thepeak noise value and offset while minimising low frequency deviation
with optimised control strategy found in the PACE controller.
Controller offset is simply the average difference between thecommanded value and the controlled pressure. Controller noise is thedeviation of the pressure around the average controlled pressure. This isshown in Figure 6 below.
0.12
0.1
0.08

Error mbar

0.06
0.04

Controller offset

0.02
0-0.02

01

2

3

4

5

67

8

9-0.04-0.06

Time (s)Commanded pressure

Controller average pressure

Figure 6: Controller offset and noise

The controller noise in the PACE products is less than 10 parts per millionof full scale. This noise is factored into the uncertainty budget for thesensor, removing the need for the system integrator to allow for this in
their error budgets. This compares favourably with 30 parts per million
control stability of similar competitive products.

8PACE CM3 High Accuracy Pressure Controller

10PACE’s modular construction
The modular nature of PACE’s construction means that existingcustomers can easily upgrade their PACE controllers from CM2 (orbelow) to the improved accuracy CM3 range with very little downtime
being incurred. There is also the added benefit that the control module
itself can be shipped to Druck for upgrade, repair or calibration by itself,
without having to remove the chassis from any rack or testbench, thus
providing further savings on downtime and maintenance costs. This also
allows for the Druck Service team to perform a health check on the entire
control module, which is not possible with some competitor’s models,
where only sensors are returned for repair/calibration.
Additional advantages of the PACE construction with respect to thecontrol modules being ‘plumbed in’ directly mean that PACE can achieve
the fastest speed to setpoint of any pressure controller, as well as being
less susceptible to leaks.
For new and existing customers, the addition of the PACE CM3 range
now brings even more flexibility to the PACE product line in terms ofprice vs performance.

Easy installation of the PACE CM3 unit

Modular PACE CM3 unit

Compatible with PACE 5000 and 6000

9PACE CM3 High Accuracy Pressure Controller

Automated Calibration and Data Integration
using Druck’s 4Sight2 Calibration
Management Software

4Sight2 Calibration
Management
Software offers
end-to-endautomatedcalibration withPACE CM3

Druck’s 4Sight2 Calibration Management Software integrates seamlessly
with its PACE pressure controller to offer end-to-end automatedcalibration. There are no manual interventions and therefore this eliminates
documentation errors and increases the quality of calibration data.
4Sight2 controls Druck’s PACE and DPI range of digital pressure
indicators and calibrators, running tests which can beinitiated with a single button click and automatically
capturing data for each test point. Results are saved
within the software to ensure the user’s calibration
process is efficient, completely integrated with their
Druck hardware and paperless. In addition thisremoves the possibility of user input/data recording
error as well as freeing up the operator to focus onother tasks simultaneously.
Furthermore, 4Sight2 calculates expanded uncertainty,
which provides greater confidence over the calibration
measurement data and helps ensure devices function within
defined limits, in accordance with industry standards. All calibration
data, drift analysis and traceability information are securely storedand are readily available, ensuring users are audit ready at all times.

Customer support and service
To maintain and keep PACE within its optimum performance range,
Druck offer customers a range of calibration and service options toprovide the peace of mind that comes from dealing with the OEM(Original Equipment Manufacturer).
For all enquiries please contact us or find local phone numbers here
The authors of this paper are:Neculai Moisoi, PhD Senior Metrologist
Neil Sands, SEng Senior Pressure Controllers Designer
Timothy Sparkes, IEng MIET Capability Development Leader
Dean Onyon, BSc Lead Electronics Design Engineer
Tom Piggin, MEng Lead Electronics Design Engineer
Nigel Scoggins, MSc Product Manager - PACE

Copyright 2024 Baker Hughes Company. All rights reserved.
BHCS38946A		

10(06/2024)

PACE CM3 High Accuracy Pressure Controller