PPS SOI Sensors
Advanced Technology SOI Sensor - Proprietary Design
Reliability, accuracy and flexibility in E-beam welded package designs and OD sizes are the cornerstone to PPS's success.
PPS Gauge models with SOI Sensors
- PPS25XM Extreme Memory Gauge
- PPS27 SOI PDMS Systems
- PPS53XM SPM Gauge
What is SOI?
SOI stands for a silicon on insulator piezoresistive sensor. PPS began introducing the advanced technology SOI sensor into its memory gauges in late 2014. Memory and permanent gauges that are made with PPS's new advanced SOI sensor are being utilized for many oil and gas projects by our customers. This is due to the state of the art SOI sensor being reliable and accurate in very hazardous and corrosive environments, without worrying about failure.
What makes the SOI Sensor so advanced?
The SOI technology enables the sensing elements to be dielectrically isolated from the substrate, and each other, via the use of a non-conductive isolation layer of silicon dioxide. This enables predictable and repeatable sensor behavior ranging from cryogenic temperatures all the way up to 400°F (204 ° C) and above. The piezoresistive SOI sensor is a truly solid state device as the force collector and sensing elements are all part of a monolithic silicon crystal structure.
SOI sensors offer true static pressure measurement capability without taking any special precautions and its drift is better than quartz according to the industry data regarding SOI technology.
Piezoelectric (Quartz) vs Piezoresistive (Silicon-Sapphire) vs Advanced Piezoresistive (SOI)
Piezoelectric sensors (Quartz, Tourmaline, and several naturally occurring crystals) are self-generating and develop electrical potential (charge) in proportion to applied pressure stress. Piezoresistive sensors are fabricated from silicon crystals.
Quartz piezoelectric sensors are effectively AC coupled devices, and as such, are incapable of measuring a true static pressure as piezoelectric material can only sense alternating force. Some lower frequency measurements (<0.5 Hz) are possible using quartz piezoelectric transducers, but the user must be aware of current drive and associated self-heating causing drift in the output of the transducer during low frequency operations.
The older generation piezoresistive sensors utilized isolation technology between the sensor network and the bulk underlying silicon based on the p-n junction. These devices are accurate and reliable at low temperatures. However when comparing older generation piezoresistive sensors with piezoelectric sensors at higher temperatures [those approaching 250° F (120 ° C)], the piezoresistive sensors fell short because the p-n junction isolation deteriorates which creates current leakage, resulting in measurements errors, lower accuracy, lower resolution, and higher drift.
The SOI sensor overcomes any high temperature issue because it is not built on the p-n junction, it is a silicon on insulator wafer where the insulator is silicon dioxide. Thereby creating a reliable piezoresistive sensor with characteristics that closely resemble a quartz peizoelectric sensor.
Comparison of SOI and Quartz characteristics table is detailed below.
Characteristics | SOI Sensor | Quartz Sensor |
| Pressure Capability | 10k psi| 20k psi | 30k psi | 10k psi| 20k psi | 30k psi |
| Pressure Accuracy | 0.01% to 0.15% FS | ± 0.02% FS |
| Pressure Resolution | 0.02 psi typical 0.03 psi | 0.015 psi typical 0.02 psi |
| Over Pressure Capability | 2X Max. Rated Pressure | 1.1X Max. Rated Pressure |
| Operating Temperature Capability | -20°C to 200°C | -20°C to 200°C |
| Over Temperature Capability | 2X Max. Rated Temperature | 1.1X Max. Rated Temperature |
| Static Pressure Capability | Yes | No |
| Dynamic Response | " 1 sec rise time | " 2 sec rise time |
| Drift | 0.01% FS/year | 0.02% FS/year |
| Total Error Band at Constant | + 0.1% FS typical | ±1% FS typical |
| Thermal Effects | ± 0.001 to 0.01% FS/°F | ± 0.03 to 0.2% FS/°F |
| Shock Performance X, Y, Z | 20,000g at 0.1 ms half sine | 500g at 0.1 ms half sine |
Application Note
Although older piezoresistive gauges and quartz piezoelectric gauges may get damaged or require re-calibration during over-pressure or over-temperature state, the PPS SOI sensor will maintain linearity with only a minor decrease in readings accuracy, and will recover instantly once the pressure and/or the temperature decreases to the normal operating range.
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