You've done the homework described in the article I wrote for Sensors titled "A Twelve-Step Sensor Selection Checklist". Now it's time to send your specification to the vendors you've chosen. You're probably working with your company's purchasing department, a process that has its pluses and minuses.
A Give-and-Take Process
Your company's buyers look to you for guidance in evaluating your specification and will often test you by suggesting you relax some of your technical requirements to get the best deal. Their priority is to get the biggest bang for your company's buck; yours is to get the best measurement device for the application. You'll reach a happy medium, but not without give and take.
Don't hesitate to speak up and make the case for adhering to the letter of your specification. If you've got an item in the spec that cannot be relaxed, stand your ground. Often, you will have to provide the buyer with chapter and verse as to why it can't be changed.
If you've over-specified the requirements, the exercise will give you a chance to rethink some of the finer points. But if you're spot on, don't give in. Make your case and earn the buyer's respect with sound technical reasoning. He or she wants to be sure you are competent, but at the same time, will negotiate with you to save time and money. That's especially true if the purchasing department has already negotiated blanket prices for similar products or if one or more of the vendors you have selected are not on the company's preferred supplier list. These days, that means the vendors have passed quality-assurance screening and are suppliers of long standing.
One of the key items to check is that the vendors offer traceable calibrations for their devices. You've already verified that about the vendors you have selected, but do the vendors on the preferred supplier list meet these requirements? You may need to work with your company buyer to ensure that suppliers added to your list have those special qualifications. If unsure, you may have to add an item to the solicitation documents requiring a sample copy of calibration certificates and traceability statements. If any of suppliers you've chosen are the key vendors for the type of sensor you are looking for, you should include supporting information in your specification to get the buyer to qualify them and request bids.
If your buyer tells you he or she can't or won't buy what you need, you have to put your foot down and insist. It can be done, even if the vendors aren't prequalified. You don't always win, but work to get what you need and cut corners only as a last resort.
You should track the bids throughout the solicitation process to ensure you hear from the people you have chosen. And don't forget to review all the exceptions to your specification proposed by bidders.
You can read more about techniques, tips, and rules for professional buyers at businessballs.com.