Thermotron provides some insight into what sort of questions a buyer of used environmental chambers for accelerated stress testing should ask.
Buying a test chamber is a big decision, and the initial considerations relate to size, temperature range and humidity capabilities. Buying a used one from a reseller requires additional due diligence. A used test chamber can save time and money in the short term, but there may be issues that could quickly negate any initial savings. What information is required to make an informed purchase?
1 How Old is the Used Chamber?
When was the chamber built? Does the seller actually know or is it just a guess? While it is true that a well-built chamber can last decades, the reality is that no matter how well a test chamber is built, the amount of time it properly functions depends on how hard and frequently the test chamber is run and its maintenance, service, and calibration history. This leads to our next two questions:
2 Was the Chamber Cared for Properly?
Service, calibration, and maintenance records are extremely important to the history of a used chamber. What work was done? When was it done? Are there records for it? Accurate service records will help determine the chamber’s condition and can help predict its reliability in the future. If the chamber had yearly calibration and preventive maintenance service, users will have a better chance of having a successful partnership with the chamber.
3 How Was the Test Chamber Used?
Certain types of environmental testing can be more strenuous than others. Sometimes, test chambers are run to the extremes, constantly ramping up and down in temperature and operating over several days or even weeks non-stop. It’s helpful to determine how the chamber was used and in what type of environment the chamber was operating. Was it in a clean lab environment or was it in a dirty and dusty manufacturing plant?
Another possible issue is that products previously tested in the chamber may have leached chemicals into the chamber, which could rust or compromise the workspace and performance. If the used test chamber has a humidity feature, what kind of water was used? If the water was not at the proper purity standards, then some of the internal tubing could be corroded.
4 What Type of Refrigerant is Used?
Regulations prohibit the use of certain types of refrigerants, which have been used to cool environmental test chambers. The Montreal Protocol banned chlorofluorocarbons (CFCs) which include many older types of refrigerants. If an environmental test chamber was built before 1995, it’s possible the chamber is cooled with banned refrigerants. In this case, it may be difficult to fix future refrigeration leaks because the refrigerant might not be commercially available. The only option for repair would be a cooling system field retrofit, which can be quite expensive. This may ultimately negate any cost savings.
5 Which Controller?
The controller is the “brains” of the chamber, and, with the right controller, the test chamber is harnessed to perform at optimal levels. Often, the controller on used test chambers is replaced with a generic controller by the third-party reseller. When this happens the chamber immediately loses some of its functionality and features, whereas the proprietary controller supplied originally will allow a full range of capabilities to be accessed.
6 Utility Requirements?
It is important to know the chamber’s electrical and voltage requirements. Is it air-cooled or water-cooled? Does it require compressed air or liquid nitrogen or CO2 supply? It could be very costly to upgrade utilities to accommodate the used chamber.
7 Who is the Reseller?
Is the seller the original owner? If the used chamber is with a reseller, then how did they acquire the chamber? They could have purchased it from the original owner, may have found it on Craigslist or bought it at an auction. Knowing who has owned the equipment is important because it gives a deeper knowledge of the chamber, including its operating environment and service history.
8 Model and Serial Numbers?
A serial number allows the manufacturer to check their records and verify how old the chamber is, who the original owner is, and any service work performed. Hopefully this information allows seller’s claims to be verified.
9 Did the Reseller Refurbish the Chamber?
If the reseller did any work on the chamber, was it a qualified, certified service engineer with experience in refurbishing test equipment who performed the upgrade? Each chamber manufacturer is different, so upgrades can be complicated. Receiving a used chamber that has not properly been refurbished can cause a lot of equipment downtime.
Does a product manual come with the purchase? If not, is it clear how to run the chamber? Is troubleshooting required to solve some problems?
Which Accelerated Stress Test (AST) Method?
AST systems perform various accelerated stress test methods such as Highly Accelerated Life Test (HALT), Highly Accelerated Stress Screen (HASS), among others. Each type of stress precipitates specific defects that might be missed by traditional testing methods and equipment.
Highly Accelerated Life Testing (HALT) applies increasingly higher levels of stress to force product failures. HALT uses multi-axis vibration and high thermal ramp rates significantly beyond the product’s normal use environment to expose product weaknesses quickly. Using high levels of stress causes a significant time compression and exposes the same failures experienced during normal use over a product’s lifetime.
Highly Accelerated Stress Screening (HASS) is a production quality screen that applies similar, but much lower stresses, to those used in HALT. HASS aims to verify that production units continue to be manufactured as designed and quickly detects component or manufacturing irregularities, prior to shipping large quantities of flawed product. This screening method is “tuned” so that it detects weak products while still leaving several, if not many, lifetimes of field use in the shipped product.
Information supplied by Thermotron based on its “Refurbished Chambers” brochure.