You open the UNIK 5000 datasheet and see four different accuracy numbers: ±0.04% FS, ±0.1% FS, a "total error band" curve, and a cryptic option code table with letters A through H. Which one actually matters for your measurement? The Druck UNIK 5000 is a modular silicon piezoresistive pressure sensor platform covering vacuum to 10,000 psi in dozens of ranges — but the accuracy figure you can trust depends entirely on which option code you order and how you interpret the fine print of the specification.
UNIK 5000 accuracy is specified three ways, and they are not interchangeable. Non-linearity, hysteresis, and repeatability (NLHR) is the tightest number — typically ±0.04% FS for the premium grade — but it only covers the sensor element's mechanical behavior under laboratory reference conditions. It excludes thermal drift. Total error band (TEB) folds in thermal zero and span shifts across the compensated temperature range (usually −10 to +50°C or −20 to +80°C depending on the option code). For outdoor or process-mounted installations, TEB is the number that governs actual measurement uncertainty, and it can be 2–3× larger than NLHR. The third figure is long-term stability, specified as ±0.05% FS per year — relevant if the pressure sensor is embedded in a test stand that is calibrated annually.
Decoding the Option Code Table
Druck uses a letter-code system to define accuracy grade, compensated temperature range, and output type in a single character. The common codes are:
- Option A
- ±0.1% FS NLHR, 0–5 V output, −10 to +50°C compensated range. This is the standard industrial grade, suitable for general-purpose hydraulic and pneumatic monitoring where the ambient temperature at the sensor body stays within a narrow band.
- Option D
- ±0.04% FS NLHR, RS-485 Modbus output, −20 to +80°C compensated range. The premium accuracy grade with digital output — no analog loop error. The wider compensated range makes this the choice for outdoor installations and aerospace test cells.
- Option G
- ±0.06% FS NLHR, 4–20 mA output, −20 to +80°C compensated range. The sweet spot for process industry: good accuracy with the noise immunity and diagnostic simplicity of a 4–20 mA loop.
- Option H
- ±0.04% FS NLHR, millivolt output (10–100 mV), −10 to +50°C compensated range. Highest raw accuracy but requires a precision voltmeter or DAQ card at the receiving end — the mV signal is susceptible to EMI, so keep cable runs short and shielded.
Pressure Range Selection and Turndown
The UNIK 5000 is available in ranges from 70 mbar (1 psi) to 700 bar (10,000 psi), but accuracy is specified as percent of full scale — which means the range you pick determines the absolute error in engineering units. A ±0.1% FS sensor with a 1000 psi range has a ±1 psi uncertainty. If your application requires sub-0.5 psi accuracy, you must either select a tighter accuracy grade (Option D) or choose a range closer to your maximum working pressure so the full-scale error maps to a smaller absolute value.
Druck specifies a 3:1 turndown — meaning a 100 psi sensor can be ranged down to 33 psi with a proportional increase in uncertainty. Beyond 3:1 the signal-to-noise ratio degrades. For applications spanning widely different pressures, running two UNIK 5000 sensors at different ranges with a selector valve is often more practical than relying on deep turndown of a single device.
What does the "hydrogen compatible" UNIK5000H variant change?
The Druck UNIK5000H uses a Hastelloy C276 diaphragm and Inconel 625 pressure port instead of the standard 316L stainless steel. Standard 316L wetted parts embrittle in hydrogen service above 1000 psi — the hydrogen molecule is small enough to diffuse into the steel lattice and form hydrides at grain boundaries, eventually causing cracking. The UNIK5000H option code specifies the nickel-alloy wetted path plus a gold-plated O-ring groove to further reduce hydrogen permeation. Accuracy is ±0.04% FS, matching the Option D grade, and the compensated temperature range is −20 to +80°C. If your application involves hydrogen compression, electrolyzer output, or fuel cell test stands, the standard UNIK 5000 is not sufficient — specifying the H variant is a safety-critical materials decision, not a performance upgrade for industrial sensor applications with aggressive media.
How does the TERPS 8000 compare to the UNIK 5000 on accuracy?
The Druck TERPS 8000 is a different technology platform: a resonant silicon pressure sensor (RPS) that measures pressure as a shift in resonant frequency rather than a strain-gauge voltage. The TERPS 8000 achieves ±0.01% FS — four times better than the UNIK 5000's best grade — and adds a built-in barometric reference for true absolute pressure measurement. The trade-off is range: the TERPS 8000 tops out at 200 bar (3000 psi), whereas the UNIK 5000 extends to 700 bar (10,000 psi). For high-accuracy, low-to-mid-range applications like turbine inlet pressure or cleanroom differential measurement, the TERPS justifies its higher price with a tenfold improvement in long-term stability (±0.005% FS per year). For general industrial pressure monitoring up to 10,000 psi, the UNIK 5000's broader range coverage and lower cost make it the more practical choice.
How often should I recalibrate a UNIK 5000?
Druck recommends annual recalibration for the ±0.04% and ±0.06% grades, and 18–24 months for the ±0.1% standard grade — assuming the sensor is operated within its specified temperature range and not exposed to pressure spikes beyond 1.5× full scale. In practice, calibration intervals should be determined by the measurement's criticality: a UNIK 5000 used as the reference transducer in a pressure calibration rig warrants a 6-month cycle with an as-found/as-left record to detect drift trends before they exceed tolerance. A sensor monitoring hydraulic clamping pressure on a machine tool can safely run on a 24-month interval. The UNIK 5000's modular design — the sensor head unscrews from the electronics housing — means recalibration can be done by swapping the head and returning it to a lab, with zero downtime and no need to break pressure-tight fittings.
