Slurry density: ultrasonic vs tuning fork — how to choose?

Steps

1. Working principle

   PS7010 passes an ultrasonic beam across the pipe and measures how much energy the medium absorbs and scatters; concentration is calibrated against that attenuation. PS7400 immerses a fork that is driven at its resonant frequency, and density follows from how much that frequency shifts as the surrounding medium loads the fork. The practical difference is what each is sensitive to. Attenuation responds to particle behaviour, so its calibration is tied to the particle size distribution it was made on; a fork responds to the bulk property, so a change in grind at constant mass concentration does not move it. Where the ore blend and grind vary, that is a real advantage for the fork.

2. Intrusiveness and abrasion

   PS7010 clamp-on has zero process exposure — no wear surface, no penetration, nothing to erode. On coarse abrasive slurry that is a decisive advantage, and it is the main reason to prefer it here. PS7400's fork sits in the stream and wears; a tungsten-carbide tip is supplied as standard rather than as an optional coating, which extends service life considerably, but on genuinely coarse duty like cyclone underflow or gravel-bearing dredge spoil, an immersed element is still the wrong architecture. Worth stating plainly: erosion of a fork shows up as a slow calibration shift rather than a clean failure, which is harder to notice than an instrument that simply stops.

3. Scaling and coating

   Both suffer from deposits, differently. A coating on the inside of the pipe attenuates the PS7010's path and biases its reading; a coating on the fork adds mass and shifts the frequency the same way added density would. Neither fails outright — both drift, which is the more dangerous mode because the reading stays plausible. Two mitigations are worth designing in rather than adding later: put the instrument where flow velocity keeps the surface swept, and schedule a periodic check against a sample so drift is detected rather than absorbed into the operator's mental model of what the reading normally is.

4. Accuracy in context

   The PS7400 is specified at ±0.001 g/cm³ with ±0.0001 g/cm³ repeatability, and the PS7010 at ±1 % FS. Those figures are not directly comparable, because they are stated against different references on different media — a full-scale percentage on a wide slurry range and an absolute figure on a liquid range describe different things. The question worth asking instead is what the reading does over a shift on your process: a fork's fine repeatability is only useful if it is not being eroded or coated, and an ultrasonic reading calibrated on the actual slurry can outperform its headline number. Ask for a calibration on your process liquid, and ask what happens between verifications.

5. Application summary

   Choose PS7010 for pipe-mounted slurry where the line cannot be tapped, the bore is DN500 or below, and bubble content is low. Choose PS7400 for tanks and vessels, for chemically aggressive but low-solids service where a coated fork solves the materials problem, and where a point measurement in a vessel is what the control scheme needs. Choose PS7000 instead of either where the bore is large, gas is present, or both — which describes most FGD absorber circuits, tailings lines and dredge discharge. If you are unsure, the deciding questions are in the six-step selection guide: can the pipe be tapped, is there gas, and how coarse is the solid.