Your "suggestion" actually isn't that far off. I haven't found any relevant refs. to "láminas de cupones", so I am assuming the whole expression refers to the "cupones" (coupons) themselves. Here are some explanations:

The Weight Loss technique is the best known and simplest of all corrosion monitoring techniques. The method involves exposing a specimen of material (the coupon) to a process environment for a given duration, then removing the specimen for analysis. The basic measurement which is determined from corrosion coupons is weight loss; the weight loss taking place over the period of exposure being expressed as corrosion rate. The simplicity of the measurement offered by the corrosion coupon is such that the coupon technique forms the baseline method of measurement in many corrosion monitoring programs. The technique is extremely versatile, since ***weight loss coupons*** can be fabricated from any commercially available alloy.
http://engrmaa.blogspot.com/2009/03/corrosion-coupon.html

(There is a picture of the coupons at the above link.)

The mainstay of most process corrosion monitoring systems is the ***weight loss coupon***, either as a back-up to other methods or, in their own right, where conditions are not so dynamic as to require proactive management. Teledyne Cormon supply a full range of cleaned, weighed and packed coupons together with holders and mounting kits for all types of process monitoring applications.
http://www.cormon.com/products/other.aspx

Other refs.
http://www.google.com/search?num=100&hl=en&rlz=1G1GGLQ_ENES3...