Gauge Installation

When bonding the strain gauge, the most suitable adhesive should be selected for each application. A typical installation procedure is described below using the fas-curing type adhesive CN.

1. Preparation

The following items are required for bonding and lead wire connection:

strain gauge
bonding adhesive
connecting terminals
solvent
cleaning tissue for industrial use
soldering iron
solder
abrasive paper (120 ... 180 grit and 240 ... 320 grit)
marking pencil
scale
tweezers
extension lead wires
polyethylene sheet
nipper
cellophane tape

2. Surface preparation

Before bonding, remove all grease, rust, paint, etc. from the bonding area. Sand an area somewhat larger than the bonding area uniformely and finely with abrasive paper. Finish the surface with #120 to 180 abrasive paper for steel, or #240 to 320 for aluminium.

Clean the bonding area with industrial tissue paper or cloth soaked in a small quantity of chemical solvent such as acetone. Continue cleaning until a new tissue or cloth comes away completely free of contamination. Following the surface preparation, be sure to attach the gauge before the surface becomes covered with an oxidizing membrane or becomes newly contaminated.

Carefully mark the position of the strain gauge with a scriber or 4H pencil. Using cellophane tape, mark off an area slightly larger than the gauge base of the strain gauge to be installed to prevent the adhesive from spreading outside the installation area (this is referred to as masking).

3. Curing

Take the gauge together with gauge binder out of the package. Move the strain gauge base and gauge leads part way out of the binder as shown in the figure. Place the gauge binder onto a clean glass slide. Use a piece of cellophane tape to stick the gauge leads and the portion of gauge base protruding from the binder in place, as shown in the figure.

Carefully peel off the strain gauge and cellophane tape and then align the gauge with the positioning marks and stick it down. Carefully peel up one end of the tape and coat the back of the strain gauge with CN adhesive. Usually one drop of adhesive will be suffice, but you may increase the number of drops according to the size of the gauge. Use the adhesive nozzle to spread the adhesive over the back surface thinly and uniformely. Place the gauge on the position mark, place a polyethylene sheet onto it and press down on the gauge constantly using your thumb or a gauge pressing device. This should be done quickly as the curing process is completed very fast. The curing time varies depending on the gauge, test specimen, temperature, humidity and pressing force. The curing time under normal conditions is 20 to 60 seconds.

4. Soldering and wiring

Once the adhesive used to bond the strain gauge has hardened, peel off the polyethylene release sheet and pull up the gauge leads. Pull up the gauge leads as far as and a little way onto the gauge base. Hold down the gauge lead anchor points on the gauge base with a pair of tweezers to ensure that you do not break the gauge leads. In the same way as the strain gauge, use the CN adhesive to install the connecting terminals close to the gauge. Lay the gauge leads over the connecting terminal, allowing a little slack in the gauge leads, and apply solder. Apply sufficient solder to the cover the metal foil on the connecting terminal. Twist the excess gauge lead off with a pair of tweezers.

Solder the lead wires to the connecting terminal. Take care not to use too much heat as this can cause the metal portions of the connecting terminal to peel off. Use a fine brush dipped in solvent to wipe away any soldering flux left behind after soldering, as flux deposits can lead to problems with connection.

Back

	Before bonding, remove all grease, rust, paint, etc. from the bonding area. Sand an area somewhat larger than the bonding area uniformely and finely with abrasive paper. Finish the surface with #120 to 180 abrasive paper for steel, or #240 to 320 for aluminium.
	Clean the bonding area with industrial tissue paper or cloth soaked in a small quantity of chemical solvent such as acetone. Continue cleaning until a new tissue or cloth comes away completely free of contamination. Following the surface preparation, be sure to attach the gauge before the surface becomes covered with an oxidizing membrane or becomes newly contaminated.
	Carefully mark the position of the strain gauge with a scriber or 4H pencil. Using cellophane tape, mark off an area slightly larger than the gauge base of the strain gauge to be installed to prevent the adhesive from spreading outside the installation area (this is referred to as masking).

Take the gauge together with gauge binder out of the package. Move the strain gauge base and gauge leads part way out of the binder as shown in the figure. Place the gauge binder onto a clean glass slide. Use a piece of cellophane tape to stick the gauge leads and the portion of gauge base protruding from the binder in place, as shown in the figure.

Carefully peel off the strain gauge and cellophane tape and then align the gauge with the positioning marks and stick it down. Carefully peel up one end of the tape and coat the back of the strain gauge with CN adhesive. Usually one drop of adhesive will be suffice, but you may increase the number of drops according to the size of the gauge. Use the adhesive nozzle to spread the adhesive over the back surface thinly and uniformely. Place the gauge on the position mark, place a polyethylene sheet onto it and press down on the gauge constantly using your thumb or a gauge pressing device. This should be done quickly as the curing process is completed very fast. The curing time varies depending on the gauge, test specimen, temperature, humidity and pressing force. The curing time under normal conditions is 20 to 60 seconds.

Once the adhesive used to bond the strain gauge has hardened, peel off the polyethylene release sheet and pull up the gauge leads. Pull up the gauge leads as far as and a little way onto the gauge base. Hold down the gauge lead anchor points on the gauge base with a pair of tweezers to ensure that you do not break the gauge leads. In the same way as the strain gauge, use the CN adhesive to install the connecting terminals close to the gauge. Lay the gauge leads over the connecting terminal, allowing a little slack in the gauge leads, and apply solder. Apply sufficient solder to the cover the metal foil on the connecting terminal. Twist the excess gauge lead off with a pair of tweezers.

Solder the lead wires to the connecting terminal. Take care not to use too much heat as this can cause the metal portions of the connecting terminal to peel off. Use a fine brush dipped in solvent to wipe away any soldering flux left behind after soldering, as flux deposits can lead to problems with connection.