Low Flow Calibration – limits

The accuracy of the flowmeter can be determined by the change in the pulses per litre value over a flow rate range selected from the calibration certificate.  (This source document is also available for download from litremeter.com.)

  • Repeatability is better than ±0.1% of reading over the top 99% of range.
  • Accuracy with linearisation is better than ±0.5% of reading.

The minimum flow rate achievable depends on many variables but can be reduced to two factors:

  • the viscosity of the fluid. The higher the viscosity, the lower the low flow rate ability.
  • the perfection of the meter dimensions and components.
  1. Standard (STD) calibration rates can be achieved 99 times out of a 100. No special selection required
  2. Low Flow (LF) calibration requires matched parts and more calibration time
  3. Ultra Low Flow (ULF) calibration requires the best parts and the most patience by our calibration engineers. It is highly unlikely we can provide a batch of ULF meters due to their scarcity.

In particular, for LF03, LF05 and LF15, we can compare the low flow limits both on a linear scale and, secondly, on a logarithmic scale, as well as in a traditional table. The respective maxima are 18, 30 and 90 litres per hour:

Describes the low flow performance of the LF15
VFF flowmeter LF15 – flow range on various viscosities STD vs. LF vs. ULF
Describes the low flow performance of the LF05
VFF flowmeter LF05 – flow range on various viscosities STD vs. LF vs. ULF
Describes the low flow performance of the LF03
VFF flowmeter LF03 – flow range on various viscosities STD vs. LF vs. ULF

These tables were all updated in August 2019; rounding of some of the flow rate values understated the flowmeters’ abilities.

Additionally, work is underway to improve availability of the LF and ULF calibration bands.  Each rotor and chamber is now pre-calibrated on a nominal viscosity when first received. In actual fact, they are not calibrated as such but the low flow is determined using a custom flow programme on our automatic calibration lab.  This low flow value then enables the chamber and rotor to be categorised into one of the three bands. When an order is received with flow range and viscosity parameters the best chamber and rotor can then be selected with a high confidence level.

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