Application Note 101

Measurement Collection Technology
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Application Note 101
What is the Real Cost of Connecting a Single Caliper to a PC?

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Many of our customers need to send data from a single caliper into their PC. Typically, these customers think that they should purchase a caliper that has a serial output so that they do not have to purchase a gage interface in order to make the caliper to PC connection. Here is the question: ''Do you think using a caliper with a serial output is the most cost effective way to connect the caliper to the PC?'' I believe the answer to this question is a strong ''No!'' Let's take a look at 3 different brands of calipers and the cost associated with connecting these gages to a PC.

The analysis is based upon calipers from Fowler, Mitutoyo and Starrett. Two of these calipers (Fowler and Starrett) have a serial output, and the Mitutoyo caliper requires a gage interface in order to connect it to the PC. What is often overlooked is the fact that a gage cable connected to a caliper needs to be considered a consumable. We have asked our customers ''How frequently do you consume these gage cables?'' The response varies from a week or two to several months. The general consensus is that gage cables need to be replaced on a periodic basis.

Our analysis indicates that after you have replaced the cable two times, the interface cost for connecting the Fowler caliper is $315; for the Starrett caliper is $324 and for the Mitutoyo caliper is $206 (this includes a MicroRidge interface).

Here is a detailed cost analysis. This analysis only reflects the cost of interfacing the device and does not include the cost of the gage itself. This table was put together on 1/19/06 and the prices reflect typical pricing at that time. Even if the pricing fluctuates a little bit, the relationships are still going to hold.

Caliper Brand	Initial Cost			1st Cable Replacement		2nd Cable Replacement		3rd Cable Replacement
Caliper Brand	Cable	Interface	Total Cost	Cable	Total	Cable	Total	Cable	Total
Fowler	105		105	105	210	105	315	105	420
Starrett	71	110*	182	71	253	71	324	71	391
Mitutoyo	39	99**	128	39	167	39	206	39	245
* Level converter from Starrett required to change caliper output signals to RS-232 voltage levels. *GageWay SM single Mitutoyo interface from MicroRidge changes Mitutoyo output format to RS-232. With the Fowler and Starrett gages, you cannot alter the output format of the gage. When you use the GageWay SM from MicroRidge with a Mitutoyo gage, you have output format options.*

Summary
When you are using a gage such as a caliper or micrometer, the cable is typically subjected to a lot of moving and flexing which eventually leads to cable failure. You should really consider the probable cost of your system over a period of time and not just the initial cost. Another thing to consider is how easy is it to use and set the caliper? Not all of the gages are the same.

One of the issues that can arise with the Starrett caliper is the fact that the output has both a carriage return and a line feed at the end of the data packet. This line feed character can cause problems in some PC applications. Typically, serial devices use a carriage return as the last character in a data packet.

Revised January 6, 2008