A buzzer plate is bought against two numbers: the frequency at which it rings, and the resistance it presents at that point. A general-purpose bridge can report one of them at a time and neither as a sorted result. This instrument is built around reading both and putting the plate into a bin.
Product overview
The HG2788 is a single-purpose bench instrument for piezoelectric buzzer plates. It measures equivalent resistance Rs and resonant frequency Fs, displays them together, and compares each against the limits set for one of seven bins. There is one model in the material; the differences a buyer chooses between are the sorting arrangement and the interface, not the measurement.
The front panel has the display at the left, a column of soft keys beside it, a direction pad and numeric keypad at the right, and the two test sockets along the lower edge. The body is 330 mm wide and weighs about 5 kg, so it sits on a bench beside a fixture rather than in a rack. The rear panel carries the HANDLER connector, the fuse and the mains inlet.
How the buzzer plate tester works
The plate is connected on a four-wire Kelvin lead. Current is delivered on one pair of conductors and the voltage is sensed on the other, so the resistance of the lead and of the socket does not add to the plate. That matters here because the quantity being read can be small: a few tens of ohms on a plate that is behaving correctly, and a reading that would otherwise move every time the lead was reseated.
The instrument drives the plate and resolves the frequency at which it resonates, reported as Fs, together with the equivalent resistance at that point, reported as Rs. Each reading is compared with the limits held for the bin. When the comparison is done the decision is available on the HANDLER connector, which is what allows a sorting machine to divert the part without an operator watching the screen.
Two display modes change what the operator sees rather than what is measured. Read-only shows the value; percentage shows it against a nominal, which is the quicker read when a line runs one plate type all shift.
How to select the right buzzer plate tester
Start with the plate drawing. The two limits it gives, one for Rs and one for Fs, decide whether a seven-bin instrument is being used as a simple pass or fail gate or as a grading machine. If the drawing only gives a window, two bins are doing the work and the rest are unused; if the customer buys plates in frequency bands, the bins map onto those bands.
Then decide how the plate leaves the test. A bench where an operator loads one plate at a time needs nothing beyond the display. A line that sorts automatically needs the HANDLER connection and a fixture that presents the plate to the sockets repeatably.
Then the interface question. The serial link is listed as an option, and it is worth having only if readings are collected on a computer. It does not change the measurement.
Finally, throughput. The three speeds are a settling-time choice, not a quality choice. A plate that reads steadily at the fastest speed can be run there; one that drifts needs the slower setting, and the reading that is stable is worth more than the one that arrives sooner.
Send the plate drawing, the limits and a sample of the part, and a configuration can be proposed against them.
Measurement limitations and selection considerations
The instrument measures one plate at a time through a lead. It is not a batch tester, and the cost of testing a tray of plates is the handling time, not the measurement time.
The reading depends on how the plate is held. Contact force, contact position and the length of the lead all shift the resonant frequency of a thin piezoelectric disc, so a fixture that locates the plate the same way every time is part of the measurement rather than an accessory. The same plate measured on two different nests will not give the same number.
The test level is set by the instrument and the material does not state it. A plate characterised on a swept impedance analyzer at a known drive level is not necessarily characterised at the same level here, so a limit transferred from one instrument to the other has to be re-established on the parts, not copied.
Piezoelectric ceramics shift with temperature. A plate measured cold, straight from a delivery box, will not read the same as one that has been running in a housing. Comparing readings taken under the same conditions is more useful than comparing single numbers across a shift.
Finally, the percentage mode is a presentation of the reading against a nominal, not a correction for it. A plate outside the nominal is still outside it; the mode only makes the departure easier to see.
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.
