PISONICS
PS7110 Series
Inline Process Refractometer
Critical angle · thin-layer interface · indifferent to colour and turbidity
Inline concentration monitoring for juice, purée and concentrate
— Sucrose · fructose · juice · purée · jam · stock —
Measured: Soluble solids (Brix) / refractive index nD
Inline concentration monitoring for juice, purée and concentrate
Process background
On a juice or purée line, concentration is both a quality specification — soluble solids, which the finished product has to meet — and a process variable: when to stop evaporating, and in what ratio to blend. It is also one of the harder liquids to measure optically, carrying pulp, fibre, pigment and air all at once.
What critical-angle refractometry brings here is that it does not need the light to get through. Light strikes the interface between prism and liquid, totally reflects beyond the critical angle, and a linear CCD reads where the shadow line falls. Pulp and pigment sit outside that thin layer; the optical path never reaches them. Dark concentrate and pulpy purée read the same as clear juice.
What the method can and cannot do here
What it can do:
- Soluble solids as Brix — evaporation end point, blend ratio, finished-product conformity
- Dark, highly turbid liquids carrying pulp and air — none of it affects the reading
- Continuous tracking — a few laboratory samples a day cannot show what happened in between
What it cannot — stated here so nobody specifies it into the wrong duty:
- Total solids including insoluble pulp — refractometry counts only the dissolved fraction
- Telling fructose from sucrose — both raise the index, and the reading is the total
- Staying accurate through pectin filming or sugar deposit — high-viscosity purée should carry a CL1 from the start
Selecting the PS7110
| Variant | Prism | Process temp. | RI range | Suits |
|---|---|---|---|---|
| PS7110-A | High-strength optical glass | 0 – 60 °C | 1.33299 – 1.51782 | Ambient, non-abrasive, span within 0–90 %Brix |
| PS7110-B | Sapphire | 0 – 70 °C | 1.33299 – 1.57041 | The default for most inline duties; 0–100 %Brix |
| PS7110-C | Sapphire | −10 – 100 °C | 1.33299 – 1.57041 | Evaporation, and points before and after pasteurisation |
The connection is sanitary: the PS7110-MT4 adapter, CIP and SIP compatible, cleaning temperature −30 to 120 °C. Where the face has to be inspected, the PS7110-MT2 / MT3 tee and cross carry sight glasses.
An evaporator outlet goes to the C variant (−10 to 100 °C); blending tanks and pre-fill points are fine on the A or B. Purée is viscous and coats, so specify the PS7110-CL1 ultrasonic cleaning unit by default — retrofitting one after the reading has drifted costs considerably more than fitting it first.
General specification:
| Item | Specification |
|---|---|
| Measured quantity | Refractive index nD, converted to concentration through a scale (%Brix or wt% / vol%) |
| Accuracy | Concentration ±0.1 %; refractive index ±0.0001; temperature ±0.5 °C |
| Resolution | Concentration 0.01 %; refractive index 0.00001; temperature 0.1 °C |
| Pressure | ≤ 1.5 MPa at the prism face |
| Cleaning temperature | −30 – 120 °C; CIP and SIP capable |
| Wetted materials | SS316L plus prism; B / C accept PTFE / Hastelloy / titanium / tantalum |
| Outputs | 4–20 mA / RS485 / RS232 / USB |
| Hazardous area | Ex ia IIC T6 Ga (intrinsically safe) |
The scale has to be built for your medium
This is the most commonly misunderstood thing about refractometry, so it goes near the front.
What is calibrated at the factory is refractive index and temperature, unit by unit in standard units. That part is independent of the medium, so several instruments agree with one another. The concentration scale, however, belongs to the medium — the curve from index to concentration is a property of one liquid, and a scale built for one medium cannot be used for another.
In practice that is three things. One: tell us the medium and you get the matching scale. Two: a change of recipe, product or process stage means a change of scale, but not a trip back to the factory — RI verification, self-service modelling from sampled laboratory values and multi-point temperature compensation are all done on site. Three: be careful with multi-component systems — the same refractive index does not mean the same concentration. Two components that move the index the same way cannot be separated by refractometry, and that duty belongs to the PS7100 spectroscopic route.
Installation and upkeep
Refractometry reads a thin layer of liquid at the prism face, so a trustworthy reading rests on two things only: whether the face is always washed by liquid that represents the process, and whether it is clean.
- The face must never point downward — a downward face collects deposit, and deposit raises no fault; it shows up only as a slow one-way drift
- In a vertical line the flow must run upward — a downward run drains when the pump stops, the prism is left uncovered, and the reading stops meaning anything
- On a horizontal line, entry from below (face up) or from the side (face vertical) are both fine; entry from the top is not permitted
- Four mounting schemes: valved bypass (recommended — service it without stopping the main line) / direct in-line (cheapest, service needs a shutdown) / pumped tank loop (steadiest conditions) / tank wall (simplest)
- 2″ and under takes the PS7110-MT1 small-bore adapter; where the face has to be inspected visually, the MT2 / MT3 tee and cross carry sight glasses
- Media that can carry grit or abrasive particles must be filtered upstream — the detection window is a wear part
The cleaning strategy belongs in the design, not in a response to a reading that has already drifted: sanitary processes use CIP and SIP directly; media that coat or film take the PS7110-CL1 ultrasonic unit for continuous cleaning; media that crystallise or deposit particles take the PS7110-CL2 high-pressure flushing unit on a timed cycle.
The instrument carries prism condition diagnostics: the position of the shadow line is the measurement, and its sharpness and contrast are a second quantity the same detector sees at the same time. A deposit blunts the edge before it shifts the position, so the instrument reports its condition before the reading is visibly wrong rather than quietly returning a plausible number. It does not replace looking at the face, though — putting that into the routine inspection is worth more than any coefficient correction applied afterwards.
Before you order
These are what decide the variant, the accessories and the scale. Sending them over is quicker than guessing from a datasheet.
- Product and stage (single-strength / concentrate / purée / jam / blend) — this sets the scale
- Brix working band and finished-product tolerance
- Process temperature, particularly the real maximum at the evaporator outlet
- Viscosity and pulp content — this decides whether a CL1 is mandatory
- Connection type and pipe size
- Whether the scale should be modelled on site from laboratory data
This page is a method and selection note, not a case study. The PS7110 has no publicly citable installed base in this industry yet, so there are no unit counts, saving percentages or payback periods here — we do not invent those. Give us the process conditions and you get a selection opinion you can check, which is worth more than a handsome case study.
In closing
The Pisonics PS7 range covers several measuring principles: acoustic impedance (PS7000), acoustic attenuation (PS7010), sound velocity (PS7020), spectroscopy (PS7100), refractometry (PS7110), Coriolis (PS7200), differential pressure (PS7300), tuning fork (PS7400) and microwave (PS7600). Different principles see different things, and selection always starts with what the duty actually needs measured.
The PS7110 series takes the critical-angle route: the measurement happens in a thin layer at the prism face, which is why colour, turbidity and bubbles do not interfere — and why the prism face has to be kept clean. Juice and purée are the textbook case of dark, turbid liquids whose control variable is nonetheless dissolved-solids concentration. Method and process line up.
For a non-standard span, special wetted materials, a hazardous-area version, or to have us build the concentration scale from your own sampled laboratory data, please get in touch with our engineering team.
