[ Home | What's New | Products | Contact | International Distributors ]
The following information is provided for customers interested in calibrating the TRH-100 Probe with their own humidity calibration equipment. Under typical use in controlled residential and commercial indoor environments, the TRH-100 Probe should not require re-calibration for 5+ years.
The TRH-100 Probe requires 5 vdc excitation at 2 ma max.
Warm-up time (the time from when 5 vdc power is applied until the humidity output signal is stable) is 100 ms.
The probe has four 24 awg insulated leads with the following colors and functions:
| Black | Signal return (ground) |
| White | 5 vdc excitation |
| Green | Humidity output signal |
| Yellow (or Red) | 30k ohm Thermistor |
CAUTION! The TRH-100 Probe does not have a reverse blocking diode. The Pace XR440 Data Logger pulses current-limited power to the TRH-100 which prevents damage if the probe is incorrectly wired.
If connecting the TRH-100 to something other than a Pace Data Logger, reversing the power and ground leads will destroy the probe, so carefully check your connections before applying power!
The Humidity output signal is approximately 0.9 vdc at 0% RH and 3.9 vdc at 100% RH. Each TRH-100 probe ships with individual scaling values typed on a label bonded to the probe's cable. The first scaling value is a negative value and represents the equivalent % RH at 0v, the second number represents the equivalent % RH at 5v. Both of these values will be outside the 0 to100 (% RH) range of the TRH-100.
Re-Calibration (to be performed only if required, typically after a long interval (years) of use)
The Low / High scaling values for the TRH-100 represent the equivalent %RH values at 0v and at 5v. Because the TRH-100's output is nominally 0.9v at 0%RH and 3.9v at 100% RH, the equivalent %RH at 0v (the TRH-100's Low scaling value) will be a negative number, and equivalent %RH at 5v will be a number above 100 (the TRH-100's High scaling value).
In order to perform a re-calibration of the TRH-100, the probe must be placed in an environment (humidity chamber) with a precisely known humidity and stable temperature near 25°C. Read and note the output voltage of the TRH-100 at a precise, stable low RH environment, and at a precise, stable high RH environment. (For example, read the TRH-100's output voltage at 20% RH and 70% RH). Then using these two Voltage vs %RH readings apply the following formulas:
Y2 = High %RH value
X2 = voltage output at High %RH
Y1 = Low %RH value
X1 = voltage output at Low %RH
Slope m = (Y2 - Y1) / (X2 - X1)
Offset b = Y1 - (m)X1
Low Scaling value = b
High Scaling value = 5(m) + b
Example:
At 20% RH, TRH-100 output voltage reads 1.5v
At 70% RH, TRH-100 output voltage reads 3.1v
Slope m = (70 - 20)/(3.1 - 1.5) = 31.25
Offset b = 20 - (31.25 * 1.5) = -26.875
New Low Scaling value = b = -26.875
New High Scaling value = 5(m) + b = (5 * 31.25) + -26.875 = 129.37
Note: for customers using an XR440 with the TRH-100, the TRH-100 output voltage can be read by changing the XR440 scaling for the RH channel to a Low value of 0 and a High value of 5. This will cause the XR440 to read the TRH-100's humidity signal in volts.
XR440 Catalog and Price List PDF: 2 MB / 16 pages 
Tel: (704) 799-0688 / Fax: (704) 799-0177 / e-mail: sales@pace-sci.com
[ Home | What's New | Products | Contact | International Distributors ]