DosiTorr®
SRG Transducer/
SRG Process manometer
Key Advantages• First autonomously working
Spinning rotor gauge (SRG)• Transfer standard accuracy, 1%rdg.
• 0.1 mbar to 5 x 10-7 mbar /0.7 Torr to 4 x 10-7 Torr, 100%linear• Drift-“free”, <1.5%/yr• 1:1 replacement for drifting,frequently failing ion gauges• Corrosion-resistant• Deposition insensitive• Sensor changeable• Super clean / sterile• All-metal, no feedthroughs in thevacuum• Consistent, designed for tool
lifetime

Applications:• Replacement or in-situcalibration of Ion Gauges• Online monitoring of insulation
vacuum0-10 VDC outRS 485

24 VDC

Introduction
The SRG Transducer is a process manometer based on Spinning Rotor
Gauge technology. Compared to other methods (hot or cold cathodes,
capacitive pressure sensors), Spinning Rotor Gauges are highly accurate,
long-term stable and do not influence the pressure signal that is measured
in any way (no temperature input / ionization / gettering / drifts etc.). The
simple geometry and a stainless-steel rotating ball that moves smoothly
via electromagnetic forces is ideal for high-purity processes with various
gases – widely corrosion resistant and deposition insensitive.
Spinning Rotor Gauges (SRGs) were previously considered complex tooperate and were therefore used almost exclusively in calibrationlaboratories. A main application was the calibration of high vacuum
measuring devices, e.g. of ionization measuring methods (4 x 10-4 Torr to
4 x 10 -7 Torr / 5 x 10-4 mbar to 5 x 10-7 mbar).

Advantages – Autonomous, high-accuracy measurement, long-term stability
DosiTorr is a new type of SRG transducer based on proven and tested
components. It works completely autonomously and for the first time offers
the advantage of integrating this technology directly into a system. Due toits function, DosiTorr meets the highest purity requirements and works
without influencing the medium to be measured. It is a direct,
mathematical / physical process that only uses the effect of decelerating
a rotating ball as a means to measure the pressure in the vacuum
chamber.
Since only electromagnetic forces interact with the rotating ball, SRGs
operate wear-free, at room temperature, have extremely long-term
stability, and do not generate any ions, plasmas, heat (thermocouples/piranis), particles, etc. that may interfere with the process. There
are no mechanically stressed components that can be deformed, such as
Inconel or ceramic membranes.

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For the first time, there is a battery function for high-accuracy applications, which ensures that therotating ball is seated in a controlled manner in every operating state to protect integrity of thegauge.
A reliable measurement is provided due to an improved readout head design. The DosiTorr
generates a magnetic field that is twice as strong (90 mT) as previously available with Spinning
Rotor Gauges. The standard rotation frequency of 615 Hz of the sphere results in a significantly
more stable suspension in the magnetic field. Both effects result in a higher tolerance to vibrations
and an often-imperfect alignment of the sensor tube.
The measuring head is magnetically shielded, typically does not influence the process, and is not
influenced by external magnetic fields.

Measurement principle
The Spinning Rotor Gauge is based on the effect that gas molecules slow down a moving body as
they are adsorbed on its surface. The statistically distributed molecules striking from all directions
are accelerated accordingly and slow down the body (momentum transfer, area-related particle fluxdensity).
The desorption of the accelerated gas molecules does not contribute to the movement of the body,as this takes place in an undirected manner and the additional energy absorbed by the molecules
is released to the walls of the vessel (molecular range approx. < 4 x 10-4 Torr / 5 x 10-4 mbar) or isreleased to other molecules (> 4 x 10-4 Torr / 5 x 10-4 mbar). At pressure in the so-called transitionarea, the gas viscosity is automatically compensated by means of an integrated temperature
measurement.
In the case of the Spinning Rotor Gauge, a simple precision ball is used as the body and thedeceleration is determined by the decrease in the rotational frequency. Factors such as themolecular mass and temperature changes are only included in the measurement in an easily
determinable root ratio, coatings only with the minimal increase in the spherical radius.
Additionally, within small limits, variable factors determine the braking of the rotating ball:
1. The “residual drag” is pre-determined at the factory and without any further setting, an error of
typically ± 2 x 10-6 Torr/mbar remains. With a fine zero-point adjustment (automated) this goesto 0. This factor is a spherical material property.
2. The "molecular drag" is the actual deceleration by the surrounding medium and proportional tothe pressure. The molecular drag contains the accommodation coefficient / calibration factor
and varies with an ideally smooth sphere (factor 1) by maximum ± 6 %. This effect results fromthe roughness of the spherical surface. With balls pre-calibrated (standard) at the factory, an
accuracy of ± 1 % of the measured value can be achieved.
It should be noted that even without setting the calibration factor or the zero-point, and even after
operating for years, the system still has a high intrinsic accuracy in high vacuum, which cannot beachieved by any other vacuum measurement method and is more than sufficient for many
applications.

Measurement RangeDue to their operating principle, Spinning Rotor Gauges can be used in pressure ranges fromatmosphere to approx. UHV. Due to geometric and electromechanical conditions, however, they
are optimized for the pressure range, in which they achieve uniquely high levels of accuracy andlong-term stability:
1 % accuracy of reading between 0.07 Torr and 7 x 10-7 Torr / 0.1 mbar and 1 x 10-6 mbar
<1 % drift per year
Measuring range in general: 7 Torr to 4 x 10-7 Torr / 10 mbar to 5 x 10-7 mbar

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Technical Data
Measurement Principle
Measurement Range
Achievable accuracy

Measurement timeLong term stability
Wetted materials
AlignmentInterfaces
Digital interfaces
Remote control / GUI
Operating TemperaturePower requirements
Compliance
Analog output
Flange Type
WeightDimensions
Power consumption
Reaction time
*Spinning Rotor Gauge
7 Torr to 4 x 10-7 Torr
10 mbar to 5 x 10-7 mbar
7 Torr to 0.07 Torr
10 mbar to 0.1 mbar approx. 10 % of reading
0.7 Torr to 7 x 10-7 Torr
0.1 mbar to 1 x 10-6 mbar 1 % of reading
1, 3, 5, 10, 20, 30 s or adaptive< 1 % drift each year
1.4404, 1.4034
Horizontal
USB Type C, Bluetooth (optional), High Density 15-polig
USB, Bluetooth (optional), RS 232, RS 485
Win7/1010 to 40 °C (50 to 104 °F)
18 to 28 VDC *2004/108/EU Electromagnetic Compatibility Directive
0 bis 10 VDC configurable with Fast mode (1s output rate)
KF 25, 8 VCR, 1/8” NPT, CF40
1250 g (44 oz)
L x B x H = 200 x 105 x 65 mm (8 x 4 x 2.5 in.)Maximum 1.5 A at 24 VDC, typically < 1 A
1sPower Source in accordance with actual Council Directives, from now and following 2004/108/EU and 2014/30/EU

About usph-instruments develops, manufactures, and sells vacuum measurement systems with unique technologies
for demanding tasks in industry, research, and science. Our guideline is to provide our customers with costeffective and application-related solutions. Our specialists each have more than 20 years of experience inmeasuring and regulating pressures in the vacuum sector. The products are developed and produced inGermany and Austria and meet the highest quality standards for measuring accuracy, sustainability, andreliability. Innovative technologies help to increase energy efficiency and thus protect the environment from
unnecessary CO2 emissions.

Specifications can be changed without further notice.

info@ph-instruments.eu

www.ph-instruments.eu+43 720 500217