Hi All,
I am just a new member and first of all I would like introduce myself. I am Kaung Myat Thu, a student from Myanmar who is now studying about wood plastic composite material. I am trying to estimate the thermal expansion of composite materials by strain gage. In the literature, they mentioned that for thermal expansion, both quarter bridge and half bridge circuit can be used. Each of them has advantages and some weakness also. But in the journal papers, mostly half bridge circuit was used. I am not clear about that. So, please may I request you all to share your knowledge about that circuits and give me suggestion which one is better to use?

Sincerely,
Kaung.

 

Welcome to All About Circuits.

I am trying to estimate the thermal expansion of composite materials by strain gage. In the literature, they mentioned that for thermal expansion, both quarter bridge and half bridge circuit can be used. Each of them has advantages and some weakness also. But in the journal papers, mostly half bridge circuit was used.

For your intended application I am going to have to agree with the journal papers. Using a half bridge configuration will likely offer you improved temperature compensation. Your concern is measuring strain as a result of temperature change you don't want errors in the actual strain measurement as a result of temperature change, your concern is what changes occur on your specimen as a result of temperature change. I believe this makes a half bridge a good choice over using a quarter bridge for your intended application.

You may want to give this a read as it gets more into detail.

4. How do I choose the right strain gage?
Once you have decided the type of strain you intend to measure (axial or bending), other considerations include sensitivity, cost, and operating conditions. For the same strain gage, changing the bridge configuration can improve its sensitivity to strain. For example, the full-bridge type I configuration is four times more sensitive than the quarter-bridge type I configuration. However, full-bridge type I requires three more strain gauges than quarter-bridge type I. It also requires access to both sides of the gauged structure. Additionally, full-bridge strain gauges are significantly more expensive than half-bridge and quarter-bridge gauges.

The link has a few tables lending to making a strain gauge decision. I am also sure you can find other white papers on the subject. This is another very good link because it gets into the importance of strain gauge physical application including surface preparation, bonding techniques and adhesives. Application technique (bonding) is going to be very important for what you are doing.

Ron

 

In general, you will get better performance from a full-bridge circuit than a half-bridge and better performance for a half-bridge than a quarter-bridge.

Since you are specifically interested in thermal effects, you want your setup to be as insensitive to thermal effects in the strain gauges themselves. That generally means at least a half-bridge configuration.

 

Thanks a lot for your kindly suggestions!