What this sector has to measure
Pharmaceutical production changes the question an instrument has to answer. Elsewhere the priority is measuring the process correctly; here the instrument also has to be cleanable, and it has to be able to demonstrate that it is clean. A transmitter with the right range and the wrong surface finish is not a borderline choice, it is a rejected one.
The consequence is that materials, surface finish, connection type and the absence of crevices are specified before performance. A hygienic connection replaces the threaded joint, an electropolished wetted surface replaces the machined one, and the instrument is mounted so that it drains rather than traps product.
Documentation carries equal weight. An instrument that will contact product is normally expected to arrive with a material certificate, a surface-finish statement and a declaration covering the materials that touch the process. Where those documents are not available for a model, the honest position is to say so at the enquiry stage rather than to discover it at qualification.
Where the instruments sit
API and bulk active production
Reactors, crystallisers, centrifuges and dryers. Measurement under agitation, often in a classified area because of solvent handling, and with wetted parts that have to tolerate aggressive chemistry as well as cleaning.
Formulation and sterile filling
The most restrictive environment. Instruments sit in clean areas, must be cleanable to a defined standard, and are frequently required to be sterilised in place. Hygienic design and documented wetted surfaces are mandatory rather than preferred.
Utilities: purified water and clean steam
Conductivity, flow, temperature and pressure on water systems and clean steam. These measurements feed the quality record, so traceability and stability over a long interval matter more than a fast response.
Packaging and secondary operations
Counting, inspection, temperature and pressure in areas with a lower hygiene classification, where standard industrial instruments are often acceptable and the cost difference is significant.
Instrumentation used in this sector
| Measurement | What is measured in this sector | Instruments commonly specified |
| Flow | Purified water, clean steam, solvents, dosing of active ingredients and CIP solution | Electromagnetic meters with hygienic liners and connections, Coriolis meters where dosing accuracy or mass is required, and vortex or differential-pressure installations for clean steam |
| Pressure | Reactor and vessel pressure, filter differential, and pressure in clean utilities | Hygienic pressure transmitters with flush diaphragms, and differential transmitters where sterilisation or cleaning has to be accommodated |
| Temperature | Reaction and crystallisation temperature, clean-steam temperature, and temperature used to compensate water flow | RTDs in hygienic thermowells, chosen for stability and traceability rather than speed; thermocouples where a fast response is required in a non-product contact point |
| Level | Reactors, buffer and hold tanks, and interface detection in extraction | Radar and guided-wave transmitters with hygienic antennas, hydrostatic transmitters where the tank is simple, and point switches for high-level protection |
| Analysis | pH, conductivity, dissolved oxygen and total organic carbon in water systems and process streams | In-line analysers and transmitters with hygienic connections, sited with attention to sample handling and to the cleaning regime |
| Environmental monitoring | Particle counts, pressure differentials between clean areas and room conditions | Airborne particle counters and differential-pressure instruments used to demonstrate the state of a controlled area |
Which of these is acceptable depends on the hygiene class of the area and on the cleaning regime the installation follows. Those two facts should be stated in the enquiry.
How to specify for a pharmaceutical process
- The hygiene class of the area and the cleaning regime. Whether the equipment is cleaned in place, sterilised in place or cleaned manually determines the connection type, the surface requirement and the temperature the instrument has to survive.
- Wetted materials and the documents that cover them. State the material specification and say which certificates have to accompany the order, because the certificate has to correspond to the delivered instrument rather than to a catalogue entry.
- Surface finish and design rather than a single number. A finish figure on the wetted face is only meaningful alongside a design that avoids crevices, dead legs and threads in the product path.
- Connection type, which is normally a hygienic clamp or a hygienic flange rather than a threaded joint, supplied to the standard the plant already uses.
- Drainability and orientation. An instrument that traps product cannot be cleaned, whatever its surface finish, so the mounting orientation belongs in the specification.
- Differential pressure across a filter or membrane, where that measurement is used to demonstrate integrity and therefore falls under the same documentation requirements as the product-contact instrument.
- Temperature range during sterilisation, which is frequently well above the normal process temperature and is the value the instrument is actually chosen against.
- Whether the measurement feeds the batch record. Where it does, stability and traceability displace speed as the selection priority, and calibration records become part of the order.
Standards and approvals that may apply
- Hygienic equipment design principles, which govern surface finish, crevice avoidance and drainability rather than any instrument specification.
- Good manufacturing practice expectations, which place the documentation obligation on the user and therefore reach back to the supplier of the instrument.
- Material contact declarations, commonly required for any wetted part in a product-contact position.
- Clean-area and clean-utility monitoring requirements, where the instrument has to demonstrate the state of the environment as well as measure the process.
- We describe what an installation may have to meet. We do not claim that a product holds an approval unless the corresponding document has been supplied to us, and where it has not, the product page says so.
Applications in this sector
