- Model
- GH880 / TR100
- Principle
- Inductive pickup with a diamond stylus and a guide shoe
- Measuring range
- Ra and Rq from 0.005 to 32 µm; Rz, Ry, Rt, Rp and Rm from 0.02 to 320 µm; display range ±160 µm
- Resolution
- 0.001 µm on the GH880; 0.01 µm on the TR100
- Parameters
- Up to 26 on the GH880, including Ra, Rq, Rz, Rzjis, Rt, Rsm, Rsk, Rku and the material-ratio family; Ra, Rz, Rq and Rt on the TR100
- Standards
- Eight editions built in, covering the GB/T, ISO, ASME, DIN and JIS families, with the available parameters differing by edition
- Sensors
- Four optional sensors for plane, curved, small-bore and deep-groove surfaces, plus the integral sensor on the TR100
- Sampling length
- 0.25 mm, 0.80 mm and 2.50 mm, with an evaluation length of one to five sampling lengths
- Interface
- Bluetooth to a mobile application and USB to a PC on the GH880
- Supply
- Internal rechargeable lithium cell with an external adapter on the GH880; rechargeable on the TR100 also
Surface roughness is asked for on drawings far more often than it is measured on the shop floor, and the reason is usually the same: the figure looks simple and the measurement turns out not to be. A portable roughness tester is what closes that gap, by putting a stylus on the surface and reading the parameter the callout names.
What makes it more than a comparator is that it produces a number, and a number can be recorded, compared and disputed - provided the basis of it travels with it.
What the instrument is
A pickup and a body. The pickup holds a diamond stylus of 5 µm tip radius behind a guide shoe, and it is the part that touches the work. The body holds the drive, the electronics, the display and the storage, and it is the part that changes between the two models in this range.
The GH880 is the instrument for inspection-room work: an inductive pickup, a colour screen showing the value and the profile together, and four interchangeable sensors for work the standard sensor cannot reach. The TR100 is the basic form, with the sensor built into the body, four parameters and a fixed measuring arrangement - the instrument for a routine check on a plane or a cylinder where those four parameters are the whole requirement.
How the measurement is made
The stylus is drawn across the surface at constant speed and its vertical movement is recorded against a datum. On a skidded pickup like these, the guide shoe rides the surface itself and sets that datum, which makes the instrument quick to place but means the shoe has to have something to ride on; inside a bore there is nothing, which is why the bore sensors are separate items.
The recorded profile is then filtered so that the long-wavelength waviness is separated from the short-wavelength roughness, and the cutoff that performs the separation is the sampling length. From the filtered profile the instrument computes the parameters - Ra as the arithmetic mean deviation, Rz as a maximum height, Rq as the root mean square, and then the wider family of spacing, slope and material-ratio parameters that the GH880 offers.
The standards, and why the edition matters
The instrument carries eight standard editions across five families - GB/T, ISO, ASME, DIN and JIS - and the material lists which parameters exist in each. The sets differ substantially. Parameters such as Rk, Rpk, Rvk, Mr1 and Rδc appear in some editions and not in others, and the definitions behind a shared name are not identical either.
That is why a callout is read as a whole. A drawing that asks for Rz is asking for Rz in the edition it names, and an instrument that computes a different edition’s Rz is answering a different question. Where the drawing names an unusual parameter, checking it against the edition list is part of the enquiry rather than an afterthought.
Sensors and the geometry they answer
The standard sensor handles planes, inclined faces, conical seats and most grooves, and it is the one that is hand-held. The other three exist for geometry it cannot reach: the curved-surface sensor for a radius above 3 mm, the small-bore sensor for bores above 2 mm to a depth of 9 mm, and the deep-groove sensor for grooves wider than 3 mm and shallower than 10 mm or steps under 10 mm high.
Where the part is smaller than the instrument, the optional measuring platform is what holds it level. That is not an accessory in the sense of a convenience: a part that cannot be presented flat to the pickup cannot be measured with a skidded instrument at all.
Measurement limitations and selection considerations
Two figures in the material cannot be taken as specification and are carried as open items rather than resolved here.
The internal bore limit for the standard sensor is given as above 9 mm in the sensor description and above 6 mm in the purchasing note, and the difference is large enough to change whether the standard sensor is usable on a job. Separately, Rsm and Rs - which are spacing parameters measured in micrometres - are printed as 1 mm, which the material itself flags as a probable typographical problem.
The material also carries a note stating that its technical data are for reference only, and the runtime and charging time of the instrument are described as not printed in full. Those are read as instructions rather than as gaps to be filled in from a similar instrument.
The limitations of the method itself are worth stating plainly. The stylus measures a line, not an area; it cannot enter a groove narrower than its tip or follow a peak sharper than its tip; and it leaves a fine trace, which matters on soft materials and on decorative finishes. Where the surface is finer than the tip can follow, or softer than the traverse can cross without marking, the measurement belongs on a coupon or in a position that will not be seen.
Ordering
The items that fix the answer are the feature to be measured, with a sketch and its smallest radius, narrowest width and deepest reach; the callout exactly as it appears on the drawing, including the standard and its edition; the target figure and the process that produces it; the material, and whether a visible trace is acceptable; the size of the part and whether a platform is needed; and whether readings have to be stored and reported. Where any part of the geometry falls outside what the standard sensor can reach, saying so at the enquiry is what decides how many sensors the quotation contains. Quantity, destination port and required delivery date complete the enquiry.
Every value below is taken from source documentation. Where a parameter is not stated in the available material it is marked as information required rather than estimated.
